{"id":667,"date":"2021-12-17T21:50:21","date_gmt":"2021-12-17T21:50:21","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/9-crustal-deformation-and-earthquakes\/"},"modified":"2025-01-21T01:03:29","modified_gmt":"2025-01-21T01:03:29","slug":"9-crustal-deformation-and-earthquakes","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/9-crustal-deformation-and-earthquakes\/","title":{"raw":"9 Crustal Deformation and Earthquakes","rendered":"9 Crustal Deformation and Earthquakes"},"content":{"raw":"[caption id=\"attachment_3347\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-e1494992495928-scaled.jpg\"><img class=\"wp-image-3347 size-large\" title=\"James St. John https:\/\/commons.wikimedia.org\/wiki\/File:Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01.jpg Pennsylvanian Honaker Trail Formation\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-e1494992495928-scaled-1.jpg\" alt=\"Roadcut outcrop of multicolor rock beds offset by a normal fault.\" width=\"1024\" height=\"527\"><\/a> Example of a normal fault in an outcrop of the Pennsylvanian Honaker Trail Formation near Moab, Utah.[\/caption]\n\n<b>KEY CONCEPTS<\/b>\n\n<b>By the end of this chapter, students should be able to:<\/b>\n<ul>\n \t<li style=\"font-weight: 400\">\n<ul>\n \t<li>Differentiate between [pb_glossary id=\"2915\"]stress[\/pb_glossary] and [pb_glossary id=\"2916\"]strain[\/pb_glossary]<\/li>\n \t<li>Identify the three major types of [pb_glossary id=\"2915\"]stress[\/pb_glossary]<\/li>\n \t<li>Differentiate between [pb_glossary id=\"2583\"]brittle[\/pb_glossary], [pb_glossary id=\"2582\"]ductile[\/pb_glossary], and [pb_glossary id=\"1449\"]elastic deformation[\/pb_glossary]<\/li>\n \t<li>Describe the geological map symbol used for [pb_glossary id=\"1453\"]strike[\/pb_glossary] and [pb_glossary id=\"1454\"]dip[\/pb_glossary] of [pb_glossary id=\"2857\"]strata[\/pb_glossary]<\/li>\n<\/ul>\n<ul>\n \t<li>Name and describe different [pb_glossary id=\"1455\"]fold[\/pb_glossary] types<\/li>\n \t<li>Differentiate the three major [pb_glossary id=\"3065\"]fault[\/pb_glossary] types and describe their associated movements<\/li>\n \t<li>Explain how [pb_glossary id=\"3079\"]elastic rebound[\/pb_glossary] relates to earthquakes<\/li>\n<\/ul>\n<ul>\n \t<li>Describe different [pb_glossary id=\"3087\"]seismic wave[\/pb_glossary] types and how they are measured<\/li>\n \t<li>Explain how humans can induce seismicity<\/li>\n \t<li>Describe how [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] work to record earthquake waves<\/li>\n \t<li>From [pb_glossary id=\"3095\"]seismograph[\/pb_glossary] records, locate the epicenter of an earthquake<\/li>\n \t<li>Explain the difference between earthquake [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] and intensity<\/li>\n \t<li>List earthquake factors that determine ground shaking and destruction<\/li>\n \t<li>Identify secondary earthquake hazards<\/li>\n \t<li>Describe notable historical earthquakes<\/li>\n<\/ul>\n<\/li>\n<\/ul>\nCrustal [pb_glossary id=\"1448\"]deformation[\/pb_glossary] occurs when applied forces exceed the internal strength of rocks, physically changing their shapes. These forces are called [pb_glossary id=\"2915\"]stress[\/pb_glossary], and the physical changes they create are called [pb_glossary id=\"2916\"]strain[\/pb_glossary].\u00a0Forces involved in [pb_glossary id=\"3383\"]tectonic[\/pb_glossary] processes as well as gravity and [pb_glossary id=\"2675\"]igneous[\/pb_glossary] [pb_glossary id=\"1965\"]pluton[\/pb_glossary] emplacement produce [pb_glossary id=\"2916\"]strains[\/pb_glossary] in rocks that include [pb_glossary id=\"1455\"]folds[\/pb_glossary], [pb_glossary id=\"1934\"]fractures[\/pb_glossary], and [pb_glossary id=\"3065\"]faults[\/pb_glossary].\u00a0When rock experiences large amounts of [pb_glossary id=\"1447\"]shear[\/pb_glossary] [pb_glossary id=\"2915\"]stress[\/pb_glossary] and breaks with rapid, [pb_glossary id=\"1452\"]brittle deformation[\/pb_glossary], energy is released in the form of [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves, commonly known as an earthquake.\n<h2><strong>9.1 Stress and Strain<\/strong><\/h2>\n[caption id=\"attachment_3348\" align=\"alignright\" width=\"341\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/stress_types.gif\"><img class=\"wp-image-603 size-full\" title=\"Source: USGS https:\/\/earthquake.usgs.gov\/learn\/glossary\/images\/stress_types.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/stress_types.gif\" alt=\"Tensional stress where dominant stresses are pulling away from the object, compressional stress where dominant stress is pushing in towards the object, and shear, where part of the object is pushed and part of the object is pulled (stresses in opposite directions)\" width=\"341\" height=\"271\"><\/a> Types of stress. Clockwise from top left: tensional stress, compressional stress, and shear stress, and some examples of resulting strain.[\/caption]\n\n<b>[pb_glossary id=\"2915\"]Stress[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> is the force exerted per unit area and <\/span><b>[pb_glossary id=\"2916\"]strain[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> is the physical change that results in response to that force. When applied [pb_glossary id=\"2915\"]stress[\/pb_glossary] is greater than the internal strength of rock, [pb_glossary id=\"2916\"]strain[\/pb_glossary] results in the form of [pb_glossary id=\"1448\"]deformation[\/pb_glossary] of the rock caused by the [pb_glossary id=\"2915\"]stress[\/pb_glossary]. \u00a0[pb_glossary id=\"2916\"]Strain[\/pb_glossary] in rocks can be represented as a change in rock volume and\/or rock shape, as well as fracturing the rock. \u00a0There are three types of [pb_glossary id=\"2915\"]stress[\/pb_glossary]: <\/span><b>[pb_glossary id=\"1445\"]tensional[\/pb_glossary]<\/b>, <b>[pb_glossary id=\"1446\"]compressional[\/pb_glossary]<\/b>, and <b>[pb_glossary id=\"1447\"]shear[\/pb_glossary]<\/b><span style=\"font-weight: 400\">. [pb_glossary id=\"1445\"]Tensional[\/pb_glossary] [pb_glossary id=\"2915\"]stress[\/pb_glossary] involves forces pulling in opposite directions, which results in [pb_glossary id=\"2916\"]strain[\/pb_glossary] that stretches and thins rock. [pb_glossary id=\"1446\"]Compressional[\/pb_glossary] [pb_glossary id=\"2915\"]stress[\/pb_glossary] involves forces pushing together, and [pb_glossary id=\"1446\"]compressional[\/pb_glossary] [pb_glossary id=\"2916\"]strain[\/pb_glossary] shows up as rock folding and thickening. [pb_glossary id=\"1447\"]Shear[\/pb_glossary] [pb_glossary id=\"2915\"]stress[\/pb_glossary] involves transverse forces; the [pb_glossary id=\"2916\"]strain[\/pb_glossary] shows up as opposing blocks or regions of material moving past each other.<\/span>\n\nTable showing types of [pb_glossary id=\"2915\"]stress[\/pb_glossary] and resulting [pb_glossary id=\"2916\"]strain[\/pb_glossary]:\n<table style=\"width: 100%\">\n<tbody>\n<tr>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 19.7349%\"><b>Type of [pb_glossary id=\"2915\"]Stress[\/pb_glossary]<\/b><\/td>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 35.3461%\"><b>Associated [pb_glossary id=\"2592\"]Plate Boundary[\/pb_glossary] type (see Ch. 2)<\/b><\/td>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 21.0604%\"><b>Resulting [pb_glossary id=\"2916\"]Strain[\/pb_glossary]<\/b><\/td>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 23.7113%\"><b>Associated [pb_glossary id=\"3065\"]fault[\/pb_glossary] and [pb_glossary id=\"3081\"]offset[\/pb_glossary] types<\/b><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;vertical-align: middle;width: 19.7349%\"><span style=\"font-weight: 400\">[pb_glossary id=\"1445\"]Tensional[\/pb_glossary]<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 35.3461%\"><span style=\"font-weight: 400\">[pb_glossary id=\"2599\"]divergent[\/pb_glossary]<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 21.0604%\"><span style=\"font-weight: 400\">Stretching and thinning<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 23.7113%\"><span style=\"font-weight: 400\">Normal<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;vertical-align: middle;width: 19.7349%\"><span style=\"font-weight: 400\">[pb_glossary id=\"1446\"]Compressional[\/pb_glossary]<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 35.3461%\"><span style=\"font-weight: 400\">[pb_glossary id=\"2600\"]convergent[\/pb_glossary]<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 21.0604%\"><span style=\"font-weight: 400\">Shortening and thickening<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 23.7113%\"><span style=\"font-weight: 400\">Reverse<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;vertical-align: middle;width: 19.7349%\"><span style=\"font-weight: 400\">[pb_glossary id=\"1447\"]Shear[\/pb_glossary]<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 35.3461%\"><span style=\"font-weight: 400\">[pb_glossary id=\"2601\"]transform[\/pb_glossary]<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 21.0604%\"><span style=\"font-weight: 400\">Tearing<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 23.7113%\"><span style=\"font-weight: 400\">[pb_glossary id=\"3076\"]Strike-slip[\/pb_glossary]<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"57\"]\n\n[caption id=\"attachment_4307\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.1-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-604\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.1 via this QR Code.[\/caption]\n<h2><strong>9.2 Deformation<\/strong><\/h2>\n[caption id=\"attachment_3349\" align=\"aligncenter\" width=\"413\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/response-of-geological-materials-to-stress.png\" rel=\"https:\/\/opentextbc.ca\/geology\/wp-content\/uploads\/sites\/110\/2015\/08\/response-of-geological-materials-to-stress.png noopener noreferrer\"><img class=\"wp-image-605\" title=\"Physical Geology by Steven Earle at https:\/\/opentextbc.ca\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-300x214.png\" alt=\"Chart demonstrating the deformation of different materials when stress is applied.\" width=\"413\" height=\"295\"><\/a> Different materials deform differently when stress is applied. Material \"A\" has relatively little deformation when undergoing large amounts of stress, before undergoing plastic deformation, and finally brittlely failing. Material \"B\" only elastically deforms before brittlely failing. Material \"C\" undergoes significant plastic deformation before finally failing brittlely.[\/caption]\n\n<span style=\"font-weight: 400\">When rocks are [pb_glossary id=\"2915\"]stressed[\/pb_glossary], the resulting [pb_glossary id=\"2916\"]strain[\/pb_glossary] can be elastic, [pb_glossary id=\"2582\"]ductile[\/pb_glossary], or [pb_glossary id=\"2583\"]brittle[\/pb_glossary]. This change is generally called <strong>[pb_glossary id=\"1448\"]deformation[\/pb_glossary]<\/strong>.\u00a0<\/span><b>Elastic\u00a0<\/b><b>[pb_glossary id=\"1448\"]deformation[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> is [pb_glossary id=\"2916\"]strain[\/pb_glossary] that is reversible after a [pb_glossary id=\"2915\"]stress[\/pb_glossary] is released. \u00a0For example, when you stretch a rubber [pb_glossary id=\"2931\"]band[\/pb_glossary], it elastically returns to its original shape after you release it. <\/span><b>[pb_glossary id=\"1450\"]Ductile deformation[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> occurs when enough [pb_glossary id=\"2915\"]stress[\/pb_glossary] is applied to a material that the changes in its shape are permanent, and the material is no longer able to revert to its original shape. For example, if you bend a metal bar too far, it can be permanently bent out of shape. <\/span>The point at which [pb_glossary id=\"1449\"]elastic deformation[\/pb_glossary] is surpassed and [pb_glossary id=\"2916\"]strain[\/pb_glossary] becomes permanent is called the <strong>[pb_glossary id=\"1451\"]yield point[\/pb_glossary]<\/strong>. In the figure, [pb_glossary id=\"1451\"]yield point[\/pb_glossary] is where the line transitions from [pb_glossary id=\"1449\"]elastic deformation[\/pb_glossary] to [pb_glossary id=\"1450\"]ductile deformation[\/pb_glossary] (the end of the dashed line). [pb_glossary id=\"1452\"]Brittle deformation[\/pb_glossary] is another critical point of no return, when rock integrity fails and the rock [pb_glossary id=\"1934\"]fractures[\/pb_glossary] under increasing [pb_glossary id=\"2915\"]stress[\/pb_glossary].\n\n<span style=\"font-weight: 400\">The type of [pb_glossary id=\"1448\"]deformation[\/pb_glossary] a rock undergoes depends on [pb_glossary id=\"3116\"]pore[\/pb_glossary] pressure, [pb_glossary id=\"2916\"]strain[\/pb_glossary] rate, rock strength, [pb_glossary id=\"2689\"]temperature[\/pb_glossary], [pb_glossary id=\"2915\"]stress[\/pb_glossary] intensity, time, and [pb_glossary id=\"2917\"]confining[\/pb_glossary] pressure. [pb_glossary id=\"3116\"]Pore[\/pb_glossary] pressure is exerted on the rock by fluids in the open spaces or [pb_glossary id=\"3116\"]pores[\/pb_glossary] embedded within rock or [pb_glossary id=\"2678\"]sediment[\/pb_glossary]. [pb_glossary id=\"2916\"]Strain[\/pb_glossary] rate measures how quickly a material is deformed. For example, applying [pb_glossary id=\"2915\"]stress[\/pb_glossary] slowly makes it is easier to bend a piece of wood without breaking it. Rock strength measures how easily a rock deforms under [pb_glossary id=\"2915\"]stress[\/pb_glossary]. [pb_glossary id=\"2839\"]Shale[\/pb_glossary] has low strength and [pb_glossary id=\"1962\"]granite[\/pb_glossary] has high strength. Removing heat, or decreasing the [pb_glossary id=\"2689\"]temperature[\/pb_glossary], makes materials more rigid and susceptible to [pb_glossary id=\"1452\"]brittle deformation[\/pb_glossary]. On the other hand, heating materials make them more [pb_glossary id=\"2582\"]ductile[\/pb_glossary] and less [pb_glossary id=\"2583\"]brittle[\/pb_glossary]. Heated glass can be bent and stretched.<\/span>\n\n<span style=\"font-weight: 400\">Table showing relationship between factors operating on rock and the resulting [pb_glossary id=\"2916\"]strains[\/pb_glossary]:<\/span>\n<table style=\"width: 786px\">\n<tbody>\n<tr>\n<td style=\"background-color: #2f89c2;text-align: center\"><b>Factor<\/b><\/td>\n<td style=\"background-color: #2f89c2;text-align: center\"><b>[pb_glossary id=\"2916\"]Strain[\/pb_glossary] Response<\/b><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 373.762px\"><span style=\"font-weight: 400\">Increase [pb_glossary id=\"2689\"]Temperature[\/pb_glossary]<\/span><\/td>\n<td style=\"text-align: center;width: 384.238px\"><span style=\"font-weight: 400\">More [pb_glossary id=\"2582\"]Ductile[\/pb_glossary]<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 373.762px\"><span style=\"font-weight: 400\">Increase [pb_glossary id=\"2916\"]Strain[\/pb_glossary] Rate<\/span><\/td>\n<td style=\"text-align: center;width: 384.238px\"><span style=\"font-weight: 400\">More [pb_glossary id=\"2583\"]Brittle[\/pb_glossary]<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 373.762px\"><span style=\"font-weight: 400\">Increase Rock Strength<\/span><\/td>\n<td style=\"text-align: center;width: 384.238px\"><span style=\"font-weight: 400\">More [pb_glossary id=\"2583\"]Brittle[\/pb_glossary]<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"58\"]\n\n[caption id=\"attachment_4308\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.2-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-606\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.2 via this QR Code.[\/caption]\n<h2><strong>9.3\u00a0 Geological Maps <\/strong><\/h2>\n<span style=\"font-weight: 400\">Geologic maps are two dimensional (2D) representations of geologic [pb_glossary id=\"2960\"]formations[\/pb_glossary] and structures at the Earth's surface, including [pb_glossary id=\"2960\"]formations[\/pb_glossary], [pb_glossary id=\"3065\"]faults[\/pb_glossary], [pb_glossary id=\"1455\"]folds[\/pb_glossary], inclined [pb_glossary id=\"2857\"]strata[\/pb_glossary], and rock types. [pb_glossary id=\"2960\"]Formations[\/pb_glossary] are recognizable rock units. Geologists use geologic maps to represent where <\/span>geologic [pb_glossary id=\"2960\"]formations[\/pb_glossary]<span style=\"font-weight: 400\">, [pb_glossary id=\"3065\"]faults[\/pb_glossary], [pb_glossary id=\"1455\"]folds[\/pb_glossary], and inclined rock units are. Geologic [pb_glossary id=\"2960\"]formations[\/pb_glossary] are recognizable, mappable rock units. \u00a0Each [pb_glossary id=\"2960\"]formation[\/pb_glossary] on the map is indicated by a color and a label.\u00a0\u00a0<\/span>For examples of geologic maps, see the Utah Geological Survey (UGS) <a href=\"http:\/\/geology.utah.gov\/apps\/intgeomap\/\"><i><\/i><span style=\"font-weight: normal !msorm\">geologic map viewer<\/span><i><span style=\"font-weight: normal !msorm\">.<\/span><\/i><\/a>\n\n[pb_glossary id=\"2960\"]Formation[\/pb_glossary] labels include symbols that follow a specific protocol. The first one or more letters are uppercase and represent the geologic time [pb_glossary id=\"2192\"]period[\/pb_glossary] of the [pb_glossary id=\"2960\"]formation[\/pb_glossary]. More than one uppercase letter indicates the [pb_glossary id=\"2960\"]formation[\/pb_glossary] is associated with multiple time [pb_glossary id=\"2192\"]periods[\/pb_glossary]. The following lowercase letters represent the [pb_glossary id=\"2960\"]formation[\/pb_glossary] name, abbreviated rock description, or both.\n<h3><b>9.3.1 Cross sections<\/b><\/h3>\n<span style=\"font-weight: 400\">Cross sections are subsurface interpretations made from surface and subsurface measurements. Maps display geology in the horizontal plane, while cross sections show subsurface geology in the vertical plane. For more information on cross sections, check out the <\/span><span style=\"font-weight: 400\"><a href=\"http:\/\/wiki.aapg.org\/Cross_section\">AAPG wiki<\/a>.<\/span>\n<h3><b>9.3.2 Strike and Dip<\/b><\/h3>\n[caption id=\"attachment_3350\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/StrikeAndDip-e1489776518258.png\"><img class=\"wp-image-607 size-medium\" title=\"Source: Paul Inkenbrandt (created using Trimble SketchUp)\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/StrikeAndDip-e1489776518258-300x247.png\" alt=\"Strike is the line a rock layer would make as it intersects a horizontal plane. Dip is the angle between the horizontal plane and the tilted beds of rock.\" width=\"300\" height=\"247\"><\/a> \u201cStrike\u201d and \u201cdip\u201d are words used to describe the orientation of rock layers with respect to North\/South and Horizontal.[\/caption]\n\n[caption id=\"attachment_3351\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Strike-and-Dip-1.jpg\"><img class=\"wp-image-608 size-medium\" title=\"from L. Cameron Mosher\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Strike-and-Dip-1-300x279.jpg\" alt=\"Strike and Dip symbol showing strike of N30E and dip of 45 to the SE.\" width=\"300\" height=\"279\"><\/a> Attitude symbol on geologic map (with compass directions for reference) showing strike of N30oE and dip of 45 to the SE.[\/caption]\n\nGeologists use a special symbol called [pb_glossary id=\"1453\"]strike[\/pb_glossary] and [pb_glossary id=\"1454\"]dip[\/pb_glossary] to represent inclined [pb_glossary id=\"2858\"]beds[\/pb_glossary]. [pb_glossary id=\"1453\"]Strike[\/pb_glossary] and [pb_glossary id=\"1454\"]dip[\/pb_glossary] map symbols look like the capital letter <span style=\"font-style: normal !msorm\"><em>T<\/em><\/span>, with a short trunk and extra-wide top line. The short trunk represents the [pb_glossary id=\"1454\"]dip[\/pb_glossary] and the top line represents the [pb_glossary id=\"1453\"]strike[\/pb_glossary]. [pb_glossary id=\"1454\"]Dip[\/pb_glossary] is the angle that a [pb_glossary id=\"2858\"]bed[\/pb_glossary] plunges into the Earth from the horizontal. A number next to the symbol represents [pb_glossary id=\"1454\"]dip[\/pb_glossary] angle. One way to visualize the [pb_glossary id=\"1453\"]strike[\/pb_glossary] is to think about a line made by standing water on the inclined layer. That line is horizontal and lies on a compass direction that has some angle with respect to true north or south (see figure). The [pb_glossary id=\"1453\"]strike[\/pb_glossary] angle is that angle measured by a special compass. E.g., N 30\u00b0 E (read north 30 degrees east) means the horizontal line points northeast at an angle of 30\u00b0 from true north. The [pb_glossary id=\"1453\"]strike[\/pb_glossary] and [pb_glossary id=\"1454\"]dip[\/pb_glossary] symbol is drawn on the map at the [pb_glossary id=\"1453\"]strike[\/pb_glossary] angle with respect to true north on the map. The [pb_glossary id=\"1454\"]dip[\/pb_glossary] of the inclined layer represents the angle down to the layer from horizontal, in the figure 45<sup>o<\/sup> SE (read dipping 45 degrees to the SE). The direction of [pb_glossary id=\"1454\"]dip[\/pb_glossary] would be the direction a ball would roll if set on the layer and released. A horizontal rock [pb_glossary id=\"2858\"]bed[\/pb_glossary] has a [pb_glossary id=\"1454\"]dip[\/pb_glossary] of 0\u00b0 and a vertical [pb_glossary id=\"2858\"]bed[\/pb_glossary] has a [pb_glossary id=\"1454\"]dip[\/pb_glossary] of 90\u00b0. [pb_glossary id=\"1453\"]Strike[\/pb_glossary] and [pb_glossary id=\"1454\"]dip[\/pb_glossary] considered together are called <strong>rock attitude<\/strong>.\n\nThis video illustrates geologic structures and associated map symbols.\n<div class=\"mceTemp\"><\/div>\n\n[caption id=\"attachment_4297\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Fold-Dip-and-Strike-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-609\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/UzZFMWH-lSQ[\/embed]\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"59\"]\n\n[caption id=\"attachment_4309\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.3-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-610\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.3 via this QR Code.[\/caption]\n<h2><strong>9.4 Folds<\/strong><\/h2>\n[caption id=\"attachment_3352\" align=\"alignright\" width=\"398\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Anticline-1-e1490325844690.png\"><img class=\"wp-image-611\" title=\"Source: Paul Inkenbrandt (By Speleotherm (Own work) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons)\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-300x147.png\" alt=\"Model of anticline. Oldest beds are in the center and youngest on the outside. The axial plane intersects the center angle of bend. The hinge line follows the line of greatest bend, where the axial plane intersects the outside of the fold.\" width=\"398\" height=\"195\"><\/a> Model of anticline. Oldest beds are in the center and youngest on the outside. The axial plane intersects the center angle of bend. The hinge line follows the line of greatest bend, where the axial plane intersects the outside of the fold.[\/caption]\n<p style=\"text-align: left\">Geologic [pb_glossary id=\"1455\"]folds[\/pb_glossary] are layers of rock that are curved or bent by [pb_glossary id=\"1450\"]ductile deformation[\/pb_glossary]. [pb_glossary id=\"1455\"]Folds[\/pb_glossary] are most commonly formed by [pb_glossary id=\"1446\"]compressional[\/pb_glossary] forces at depth, where hotter temperatures and higher [pb_glossary id=\"2917\"]confining[\/pb_glossary] pressures allow [pb_glossary id=\"1450\"]ductile deformation[\/pb_glossary] to occur.<\/p>\n[pb_glossary id=\"1455\"]Folds[\/pb_glossary] are described by the orientation of their axes, [pb_glossary id=\"1456\"]axial planes[\/pb_glossary], and limbs. The plane that splits the [pb_glossary id=\"1455\"]fold[\/pb_glossary] into two halves is known as the <strong>[pb_glossary id=\"1456\"]axial plane[\/pb_glossary]<\/strong>. The <strong>[pb_glossary id=\"1456\"]fold axis[\/pb_glossary]<\/strong> is the line along which the bending occurs and is where the [pb_glossary id=\"1456\"]axial plane[\/pb_glossary] intersects the folded [pb_glossary id=\"2857\"]strata[\/pb_glossary]. The <strong>[pb_glossary id=\"1456\"]hinge line[\/pb_glossary]<\/strong> follows the line of greatest bend in a [pb_glossary id=\"1455\"]fold[\/pb_glossary]. The two sides of the [pb_glossary id=\"1455\"]fold[\/pb_glossary] are the [pb_glossary id=\"1455\"]fold[\/pb_glossary] <strong>limbs<\/strong>.\n\n<strong>Symmetrical [pb_glossary id=\"1455\"]folds[\/pb_glossary]<\/strong> have a vertical [pb_glossary id=\"1456\"]axial plane[\/pb_glossary] and limbs have equal but opposite dips. <strong>Asymmetrical [pb_glossary id=\"1455\"]folds[\/pb_glossary]<\/strong> have dipping, non-vertical [pb_glossary id=\"1456\"]axial planes[\/pb_glossary], where the limbs [pb_glossary id=\"1454\"]dip[\/pb_glossary] at different angles. <strong>Overturned [pb_glossary id=\"1455\"]folds[\/pb_glossary]<\/strong> have steeply dipping [pb_glossary id=\"1456\"]axial planes[\/pb_glossary] and the limbs [pb_glossary id=\"1454\"]dip[\/pb_glossary] in the same direction but usually at different [pb_glossary id=\"1454\"]dip[\/pb_glossary] angles. <strong>Recumbent [pb_glossary id=\"1455\"]folds[\/pb_glossary]<\/strong> have horizontal or nearly horizontal [pb_glossary id=\"1456\"]axial planes[\/pb_glossary]. When the [pb_glossary id=\"1456\"]axis[\/pb_glossary] of the [pb_glossary id=\"1455\"]fold[\/pb_glossary] plunges into the ground, the [pb_glossary id=\"1455\"]fold[\/pb_glossary] is called a <strong>plunging [pb_glossary id=\"1455\"]fold[\/pb_glossary]<\/strong>. [pb_glossary id=\"1455\"]Folds[\/pb_glossary] are classified into five categories: [pb_glossary id=\"1457\"]anticline[\/pb_glossary], [pb_glossary id=\"1458\"]syncline[\/pb_glossary], [pb_glossary id=\"1459\"]monocline[\/pb_glossary], [pb_glossary id=\"1460\"]dome[\/pb_glossary], and [pb_glossary id=\"1461\"]basin[\/pb_glossary].\n<h3><b>9.4.1 Anticline<\/b><\/h3>\n[caption id=\"attachment_3353\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/17177576122_b63f2ee137_o.jpg\" target=\"_blank\" rel=\"https:\/\/www.flickr.com\/photos\/utahgeologicalsurvey\/17177576122\/ noopener noreferrer\"><img class=\"wp-image-612 size-medium\" title=\"Source: Utah Geological Survey https:\/\/www.flickr.com\/photos\/utahgeologicalsurvey\/17177576122\/\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/17177576122_b63f2ee137_o-300x237.jpg\" alt=\"Oblique aerial photograph of an anticline in Utah. The rock beds are dipping in opposite directions on either side of the anticline's axis.\" width=\"300\" height=\"237\"><\/a> Oblique view of the Virgin Anticline (bottom right of photo) looking north. The anticline is plunging into the ground to the north. Units from youngest to oldest Jn = Jurassic Navajo Sandstone; Jk = Jurassic Kayenta Formation; Trc = Triassic Chinle Formation; Trm = Triassic Moenkopi; Pk = Permian Kaibab Formation.[\/caption]\n\n[pb_glossary id=\"1457\"]Anticlines[\/pb_glossary] are arch-like, or <span style=\"font-style: normal !msorm\">A<\/span>-shaped, [pb_glossary id=\"1455\"]folds[\/pb_glossary] that are convex-upward in shape. They have downward curving limbs and [pb_glossary id=\"2858\"]beds[\/pb_glossary] that [pb_glossary id=\"1454\"]dip[\/pb_glossary] down and away from the central [pb_glossary id=\"1456\"]fold axis[\/pb_glossary]. In [pb_glossary id=\"1457\"]anticlines[\/pb_glossary], the oldest rock [pb_glossary id=\"2857\"]strata[\/pb_glossary] are in the center of the [pb_glossary id=\"1455\"]fold[\/pb_glossary], along the [pb_glossary id=\"1456\"]axis[\/pb_glossary], and the younger [pb_glossary id=\"2858\"]beds[\/pb_glossary] are on the outside. Since geologic maps show the intersection of surface topography with underlying geologic structures, an [pb_glossary id=\"1457\"]anticline[\/pb_glossary] on a geologic map can be identified by both the attitude of the [pb_glossary id=\"2857\"]strata[\/pb_glossary] forming the [pb_glossary id=\"1455\"]fold[\/pb_glossary] and the older age of the rocks inside the [pb_glossary id=\"1455\"]fold[\/pb_glossary]. An <strong>antiform<\/strong> has the same shape as an [pb_glossary id=\"1457\"]anticline[\/pb_glossary], but the relative ages of the [pb_glossary id=\"2858\"]beds[\/pb_glossary] in the [pb_glossary id=\"1455\"]fold[\/pb_glossary] cannot be determined. [pb_glossary id=\"3338\"]Oil[\/pb_glossary] geologists are interested in [pb_glossary id=\"1457\"]anticlines[\/pb_glossary] because they can form [pb_glossary id=\"3338\"]oil[\/pb_glossary] [pb_glossary id=\"3342\"]traps[\/pb_glossary], where [pb_glossary id=\"3338\"]oil[\/pb_glossary] migrates up along the limbs of the [pb_glossary id=\"1455\"]fold[\/pb_glossary] and accumulates in the high point along the [pb_glossary id=\"1456\"]fold axis[\/pb_glossary].\n<h3><b>9.4.2 Syncline<\/b><\/h3>\n<div class=\"sketchfab-embed-wrapper\">\n\n[embed]https:\/\/sketchfab.com\/models\/3f0259ea2c6b4807a32fe3c950d13324\/embed[\/embed]\n<p style=\"font-size: 13px;font-weight: normal;margin: 5px;color: #4a4a4a;text-align: center\"><a style=\"font-weight: bold;color: #1caad9\" href=\"https:\/\/sketchfab.com\/models\/3f0259ea2c6b4807a32fe3c950d13324?utm_medium=embed&amp;utm_source=website&amp;utm_campain=share-popup\" target=\"_blank\" rel=\"noopener noreferrer\">Synclinal fold - Macigno Formation<\/a>\nby <a style=\"font-weight: bold;color: #1caad9\" href=\"https:\/\/sketchfab.com\/alanpitts?utm_medium=embed&amp;utm_source=website&amp;utm_campain=share-popup\" target=\"_blank\" rel=\"noopener noreferrer\">alanpitts<\/a> on <a style=\"font-weight: bold;color: #1caad9\" href=\"https:\/\/sketchfab.com?utm_medium=embed&amp;utm_source=website&amp;utm_campain=share-popup\" target=\"_blank\" rel=\"noopener noreferrer\">Sketchfab<\/a><\/p>\n\n\n[caption id=\"attachment_4303\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Synclinal-Fold-Element-QR-Code.png\"><img class=\"size-thumbnail wp-image-613\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this interactive activity via this QR Code.[\/caption]\n\n<\/div>\n[pb_glossary id=\"1458\"]Synclines[\/pb_glossary] are [pb_glossary id=\"3183\"]trough[\/pb_glossary]-like, or U shaped, [pb_glossary id=\"1455\"]folds[\/pb_glossary] that are concave-upward in shape. They have [pb_glossary id=\"2858\"]beds[\/pb_glossary] that [pb_glossary id=\"1454\"]dip[\/pb_glossary] down and in toward the central [pb_glossary id=\"1456\"]fold axis[\/pb_glossary]. In [pb_glossary id=\"1458\"]synclines[\/pb_glossary], older rock is on the outside of the [pb_glossary id=\"1455\"]fold[\/pb_glossary] and the youngest rock is inside of the [pb_glossary id=\"1456\"]fold axis[\/pb_glossary]. A <strong>synform<\/strong> has the shape of a [pb_glossary id=\"1458\"]syncline[\/pb_glossary] but like an antiform, does not have distinguishable age zones.\n<h3><b>9.4.3 Monocline<\/b><\/h3>\n[caption id=\"attachment_3354\" align=\"alignright\" width=\"403\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/monocline-example.jpg\"><img class=\"wp-image-614\" title=\"Source: Utah Geological Survey https:\/\/www.flickr.com\/photos\/utahgeologicalsurvey\/16596756273\/\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-300x221.jpg\" alt=\"Oblique aerial photograph of a long line of multicolored rock beds dipping into the ground. The beds are fractured and erode in a way that makes the parts sticking out look like triangles.\" width=\"403\" height=\"297\"><\/a> Oblique aerial photograph of Capitol Reef National Park's Water Pocket fold. The perspective is looking southwest toward 50-Mile Mountain and Navajo Mountain.[\/caption]\n\n<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"1459\"]Monoclines[\/pb_glossary]<\/strong> are step-like [pb_glossary id=\"1455\"]folds[\/pb_glossary], in which flat rocks are upwarped or downwarped, then continue flat. [pb_glossary id=\"1459\"]Monoclines[\/pb_glossary] are relatively common on the Colorado Plateau where they form \u201c[pb_glossary id=\"2898\"]reefs[\/pb_glossary],\u201d which are ridges that act as topographic barriers and should not be confused with ocean [pb_glossary id=\"2898\"]reefs[\/pb_glossary] (see\u00a0<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>). Capitol [pb_glossary id=\"2898\"]Reef[\/pb_glossary] is an example of a [pb_glossary id=\"1459\"]monocline[\/pb_glossary] in Utah. [pb_glossary id=\"1459\"]Monoclines[\/pb_glossary] can be caused by bending of shallower sedimentary [pb_glossary id=\"2857\"]strata[\/pb_glossary] as [pb_glossary id=\"3065\"]faults[\/pb_glossary] grow below them. These [pb_glossary id=\"3065\"]faults[\/pb_glossary] are commonly called \"blind [pb_glossary id=\"3065\"]faults[\/pb_glossary]\" because they end before reaching the surface and can be either normal or [pb_glossary id=\"3073\"]reverse faults[\/pb_glossary].<\/span>\n<h3><b>9.4.4 Dome<\/b><\/h3>\n[caption id=\"attachment_3355\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/swell-dome-scaled.jpg\"><img class=\"wp-image-3355 size-medium\" title=\"From NASA. https:\/\/eol.jsc.nasa.gov\/SearchPhotos\/photo.pl?mission=ISS006&amp;amp;roll=E&amp;amp;frame=31497\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/swell-dome-scaled-1.jpg\" alt=\"View of a dome in Utah from space. The photo shows upwarped beds of rock, where the center of the dome has been eroded away.\" width=\"300\" height=\"204\"><\/a> View of the San Rafael Swell from space. In this photograph, north is to the left. Dipping beds of rock will have lines of shadow around them. Note that the center part of the dome is eroded away.[\/caption]\n\n<span style=\"font-weight: 400\">A [pb_glossary id=\"1460\"]dome[\/pb_glossary] is a symmetrical to semi-symmetrical upwarping of rock [pb_glossary id=\"2858\"]beds[\/pb_glossary]. [pb_glossary id=\"1460\"]Domes[\/pb_glossary] have a shape like an inverted bowl, similar to an architectural [pb_glossary id=\"1460\"]dome[\/pb_glossary] on a building. Examples of [pb_glossary id=\"1460\"]domes[\/pb_glossary] in Utah include the San Rafael Swell, Harrisburg Junction [pb_glossary id=\"1460\"]Dome[\/pb_glossary], and Henry Mountains<\/span><span style=\"font-weight: 400\">. [pb_glossary id=\"1460\"]Domes[\/pb_glossary] are formed from compressional forces, underlying [pb_glossary id=\"2675\"]igneous[\/pb_glossary] intrusions<\/span><span style=\"font-weight: 400\"> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>), by salt diapirs, or even impacts, like upheaval [pb_glossary id=\"1460\"]dome[\/pb_glossary] in Canyonlands National Park.<\/span>\n<h3><b>9.4.5 Basin<\/b><\/h3>\n[caption id=\"attachment_3356\" align=\"alignright\" width=\"201\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.4_Denver_Basin_Location_Map.png\"><img class=\"wp-image-616\" title=\"By Daniel H. Knepper, Jr. (editor), US Geological Survey (http:\/\/pubs.usgs.gov\/circ\/c1219\/) [Public domain], via Wikimedia Commons https:\/\/commons.wikimedia.org\/wiki\/File:Denver_Basin_Location_Map.png\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map-184x300.png\" alt=\"Schematic map of the Denver Basin, a sedimentary basin under Denver Colorado. The map includes a cross section of the area, showing beds arching into a syncline.\" width=\"201\" height=\"328\"><\/a> The Denver Basin is an active sedimentary basin at the eastern extent of the Rocky Mountains. As sediment accumulates, the basin subsides, creating a basin-shape of beds that are all dipping towards the center of the basin.[\/caption]<span style=\"font-weight: 400\">A [pb_glossary id=\"1461\"]basin[\/pb_glossary] is the inverse of a [pb_glossary id=\"1460\"]dome[\/pb_glossary], a bowl-shaped depression in a rock [pb_glossary id=\"2858\"]bed[\/pb_glossary]. The Uinta [pb_glossary id=\"1461\"]Basin[\/pb_glossary] in Utah is an example of a [pb_glossary id=\"1461\"]basin[\/pb_glossary]. Some structural basins are also [pb_glossary id=\"1463\"]sedimentary basins[\/pb_glossary] that collect large quantities of sediment over time. Sedimentary basins can form as a result of folding but are much more commonly produced in mountain building, forming between mountain blocks or via [pb_glossary id=\"3065\"]faulting[\/pb_glossary]. Regardless of the cause, as the [pb_glossary id=\"1461\"]basin[\/pb_glossary] sinks or subsides, it can accumulate more [pb_glossary id=\"2678\"]sediment[\/pb_glossary]\u00a0because the weight of the [pb_glossary id=\"2678\"]sediment[\/pb_glossary] causes more [pb_glossary id=\"1464\"]subsidence[\/pb_glossary] in a positive-feedback loop. There are active [pb_glossary id=\"1463\"]sedimentary basins[\/pb_glossary] all over the world<\/span>. An example of a rapidly subsiding [pb_glossary id=\"1461\"]basin[\/pb_glossary] in Utah is the Oquirrh [pb_glossary id=\"1461\"]Basin[\/pb_glossary], dated to the Pennsylvanian-[pb_glossary id=\"1428\"]Permian[\/pb_glossary] age, which has accumulated over 9,144 m (30,000 ft) of [pb_glossary id=\"2852\"]fossiliferous[\/pb_glossary] [pb_glossary id=\"2834\"]sandstones[\/pb_glossary], [pb_glossary id=\"2839\"]shales[\/pb_glossary], and [pb_glossary id=\"2851\"]limestones[\/pb_glossary]. These [pb_glossary id=\"2857\"]strata[\/pb_glossary] can be seen in the Wasatch Mountains along the east side of Utah Valley, especially on Mt. Timpanogos and in Provo Canyon.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"60\"]\n\n[caption id=\"attachment_4310\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.4-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-617\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.4 via this QR Code.[\/caption]\n<h2>9.5 Faults<\/h2>\n[caption id=\"attachment_3357\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/normfaultLABEL.gif\"><img class=\"wp-image-618 size-full\" title=\"Source: USGS https:\/\/geomaps.wr.usgs.gov\/parks\/deform\/normfaultLABEL.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/normfaultLABEL.gif\" alt=\"Block diagram of a normal fault.\" width=\"300\" height=\"172\"><\/a> Common terms used for normal faults. Normal faults form when the hanging wall move down relative to the footwall.[\/caption]\n\n[pb_glossary id=\"3065\"]Faults[\/pb_glossary] are the places in the [pb_glossary id=\"2580\"]crust[\/pb_glossary] where [pb_glossary id=\"1452\"]brittle deformation[\/pb_glossary] occurs as two blocks of rocks move relative to one another. Normal and [pb_glossary id=\"3073\"]reverse faults[\/pb_glossary] display vertical, also known as [pb_glossary id=\"3066\"]dip-slip[\/pb_glossary], motion. [pb_glossary id=\"3066\"]Dip-slip[\/pb_glossary] motion consists of relative up-and-down movement along a dipping [pb_glossary id=\"3065\"]fault[\/pb_glossary] between two blocks, the [pb_glossary id=\"3067\"]hanging wall[\/pb_glossary] and [pb_glossary id=\"3068\"]footwall[\/pb_glossary]. In a [pb_glossary id=\"3066\"]dip-slip[\/pb_glossary] [pb_glossary id=\"2664\"]system[\/pb_glossary], the [pb_glossary id=\"3068\"]footwall[\/pb_glossary] is below the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane and the [pb_glossary id=\"3067\"]hanging wall[\/pb_glossary] is above the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane. A good way to remember this is to imagine a [pb_glossary id=\"3324\"]mine[\/pb_glossary] tunnel running along a [pb_glossary id=\"3065\"]fault[\/pb_glossary]; the [pb_glossary id=\"3067\"]hanging wall[\/pb_glossary] would be where a miner would hang a lantern and the [pb_glossary id=\"3068\"]footwall[\/pb_glossary] would be at the miner\u2019s feet.\n\n[pb_glossary id=\"3065\"]Faulting[\/pb_glossary] as a term refers to rupture of rocks. Such ruptures occur at [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries but can also occur in [pb_glossary id=\"2591\"]plate[\/pb_glossary] interiors as well. [pb_glossary id=\"3065\"]Faults[\/pb_glossary] slip along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane. The [pb_glossary id=\"3107\"]fault scarp[\/pb_glossary] is the [pb_glossary id=\"3081\"]offset[\/pb_glossary] of the surface produced where the [pb_glossary id=\"3065\"]fault[\/pb_glossary] breaks through the surface. [pb_glossary id=\"3069\"]Slickensides[\/pb_glossary] are polished, often grooved surfaces along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane created by friction during the movement.\n\nA [pb_glossary id=\"1934\"]joint[\/pb_glossary] or [pb_glossary id=\"1934\"]fracture[\/pb_glossary] is a plane of [pb_glossary id=\"1452\"]brittle deformation[\/pb_glossary] in rock created by movement that is not [pb_glossary id=\"3081\"]offset[\/pb_glossary] or [pb_glossary id=\"1447\"]sheared[\/pb_glossary]. [pb_glossary id=\"1934\"]Joints[\/pb_glossary] can result from many processes, such as cooling, depressurizing, or folding. [pb_glossary id=\"1934\"]Joint[\/pb_glossary] systems may be regional affecting many square miles.\n<h3>9.5.1 Normal Faults<\/h3>\nNormal [pb_glossary id=\"3065\"]faults[\/pb_glossary] move by a vertical motion where the hanging-wall moves downward relative to the [pb_glossary id=\"3068\"]footwall[\/pb_glossary] along the [pb_glossary id=\"1454\"]dip[\/pb_glossary] of the [pb_glossary id=\"3065\"]fault[\/pb_glossary]. Normal [pb_glossary id=\"3065\"]faults[\/pb_glossary] are created by [pb_glossary id=\"1445\"]tensional[\/pb_glossary] forces in the crust. Normal faults and tensional forces commonly occur at [pb_glossary id=\"2599\"]divergent[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries, where the [pb_glossary id=\"2580\"]crust[\/pb_glossary] is being stretched by [pb_glossary id=\"1445\"]tensional[\/pb_glossary] [pb_glossary id=\"1445\"]stresses[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). Examples of normal [pb_glossary id=\"3065\"]faults[\/pb_glossary] in Utah are the Wasatch [pb_glossary id=\"3065\"]Fault[\/pb_glossary], the Hurricane [pb_glossary id=\"3065\"]Fault[\/pb_glossary], and other [pb_glossary id=\"3065\"]faults[\/pb_glossary] bounding the valleys in the [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] province.\n\n[caption id=\"attachment_3358\" align=\"aligncenter\" width=\"418\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-300x199-1.jpg\"><img class=\"wp-image-619\" title=\"James St. John https:\/\/commons.wikimedia.org\/wiki\/File:Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01.jpg Pennsylvanian Honaker Trail Formation\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-300x199-1.jpg\" alt=\"Roadcut outcrop of multicolor rock beds offset by a normal fault.\" width=\"418\" height=\"277\"><\/a> Example of a normal fault in an outcrop of the Pennsylvanian Honaker Trail Formation near Moab, Utah.[\/caption]\n\n&nbsp;\n\n[caption id=\"attachment_3359\" align=\"alignleft\" width=\"351\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Horst-Graben.svg_.png\"><img class=\"wp-image-3359\" title=\"By Horst_graben.jpg: U.S. Geological Survey derivative work: Gregors (talk) 11:17, 7 June 2011 (UTC) (Horst_graben.jpg) [Public domain], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Horst-Graben.svg_-1.png\" alt=\"While the area extends, individual grabens drop down relative to the horsts.\" width=\"351\" height=\"180\"><\/a> Faulting that occurs in the crust under tensional stress.[\/caption][pb_glossary id=\"2626\"]Grabens[\/pb_glossary], [pb_glossary id=\"2625\"]horsts[\/pb_glossary], and [pb_glossary id=\"3071\"]half-grabens[\/pb_glossary] are blocks of [pb_glossary id=\"2580\"]crust[\/pb_glossary] or rock bounded by normal [pb_glossary id=\"3065\"]faults[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). [pb_glossary id=\"2626\"]Grabens[\/pb_glossary] drop down relative to adjacent blocks and create valleys. [pb_glossary id=\"2625\"]Horsts[\/pb_glossary] rise up relative to adjacent down-dropped blocks and become areas of higher topography. Where occurring together, [pb_glossary id=\"2625\"]horsts[\/pb_glossary] and [pb_glossary id=\"2626\"]grabens[\/pb_glossary] create a symmetrical pattern of valleys surrounded by normal [pb_glossary id=\"3065\"]faults[\/pb_glossary] on both sides and mountains. [pb_glossary id=\"3071\"]Half-grabens[\/pb_glossary] are a one-sided version of a [pb_glossary id=\"2625\"]horst[\/pb_glossary] and [pb_glossary id=\"2626\"]graben[\/pb_glossary], where blocks are tilted by a [pb_glossary id=\"3070\"]normal fault[\/pb_glossary] on one side, creating an asymmetrical valley-mountain arrangement. The mountain-valleys of the [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] Province of Western Utah and Nevada consist of a series of full and [pb_glossary id=\"3071\"]half-grabens[\/pb_glossary] from the Salt Lake Valley to the Sierra Nevada Mountains.\n\nNormal [pb_glossary id=\"3065\"]faults[\/pb_glossary] do not continue clear into the [pb_glossary id=\"2586\"]mantle[\/pb_glossary].\u00a0 In the [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] Province, the [pb_glossary id=\"1454\"]dip[\/pb_glossary] of a [pb_glossary id=\"3070\"]normal fault[\/pb_glossary] tends to decrease with depth, i.e., the [pb_glossary id=\"3065\"]fault[\/pb_glossary] angle becomes shallower and more horizontal as it goes deeper. Such decreasing dips happen when large amounts of [pb_glossary id=\"1445\"]extension[\/pb_glossary] occur along very low-angle normal [pb_glossary id=\"3065\"]faults[\/pb_glossary], known as <strong>detachment [pb_glossary id=\"3065\"]faults[\/pb_glossary]<\/strong>. The normal [pb_glossary id=\"3065\"]faults[\/pb_glossary] of the [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary], produced by [pb_glossary id=\"1445\"]tension[\/pb_glossary] in the [pb_glossary id=\"2580\"]crust[\/pb_glossary], appear to become detachment [pb_glossary id=\"3065\"]faults[\/pb_glossary] at greater depths.\n<h3>9.5.2 Reverse Faults<\/h3>\n[caption id=\"attachment_3360\" align=\"alignleft\" width=\"290\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/reversefaultLABEL.gif\"><img class=\"wp-image-621 size-full\" title=\"Source: USGS https:\/\/geomaps.wr.usgs.gov\/parks\/deform\/reversefaultLABEL.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/reversefaultLABEL.gif\" alt=\"Block diagram of a thrust fault, where the hangingwall overlies the footwall.\" width=\"290\" height=\"157\"><\/a> Simplified block diagram of a reverse fault.[\/caption]\n\nIn [pb_glossary id=\"3073\"]reverse faults[\/pb_glossary], [pb_glossary id=\"1446\"]compressional[\/pb_glossary] forces cause the [pb_glossary id=\"3067\"]hanging wall[\/pb_glossary] to move up relative to the [pb_glossary id=\"3068\"]footwall[\/pb_glossary]. A [pb_glossary id=\"3074\"]thrust fault[\/pb_glossary] is a [pb_glossary id=\"3073\"]reverse fault[\/pb_glossary] where the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane has a low [pb_glossary id=\"1454\"]dip[\/pb_glossary] angle of less than 45\u00b0. Thrust [pb_glossary id=\"3065\"]faults[\/pb_glossary] carry older rocks on top of younger rocks and can even cause repetition of rock units in the [pb_glossary id=\"2859\"]stratigraphic[\/pb_glossary] record.\n\n[pb_glossary id=\"2600\"]Convergent[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries with [pb_glossary id=\"2602\"]subduction[\/pb_glossary] zones create a special type of \u201creverse\u201d [pb_glossary id=\"3065\"]fault[\/pb_glossary] called a [pb_glossary id=\"3075\"]megathrust[\/pb_glossary] [pb_glossary id=\"3065\"]fault[\/pb_glossary] where denser [pb_glossary id=\"2581\"]oceanic crust[\/pb_glossary] drives down beneath less dense overlying [pb_glossary id=\"2580\"]crust[\/pb_glossary]. [pb_glossary id=\"3075\"]Megathrust[\/pb_glossary] [pb_glossary id=\"3065\"]faults[\/pb_glossary] cause the largest [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] earthquakes yet measured and commonly cause [pb_glossary id=\"1933\"]massive[\/pb_glossary] destruction and [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary].\n\n[caption id=\"attachment_3361\" align=\"aligncenter\" width=\"317\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/1280px-Thrust_system_en.jpg\"><img class=\"wp-image-622\" title=\"Source: USGS https:\/\/geomaps.wr.usgs.gov\/parks\/deform\/reversefaultLABEL.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-300x124.jpg\" alt=\"Block diagram of a thrust fault, where the hangingwall overlies the footwall.\" width=\"317\" height=\"131\"><\/a> Terminology of thrust faults (low-angle reverse faults). A klippe is the remnant of the hangingwall (aka nappe), where the surrounding material has been eroded away. A window is where part of the hangingwall has been eroded away to expose the footwall (autochton). Note the symbol shows flags on the overlying thrust plate.[\/caption]\n\n[caption id=\"attachment_3362\" align=\"aligncenter\" width=\"357\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/814080386_b34c44cfe6_z.jpg\"><img class=\"wp-image-623\" title=\"Photo by Ron Schott: \" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/814080386_b34c44cfe6_z.jpg\" alt=\"Beds of rock offset along a fault plane to where one section of the rock has been pushed up over itself.\" width=\"357\" height=\"238\"><\/a> Ketobe Knob in the San Rafael Swell of Utah displays an example of a thrust fault.[\/caption]\n\n&nbsp;\n<h3>9.5.3\u00a0 Strike-slip Faults<\/h3>\n[pb_glossary id=\"3076\"]Strike-slip[\/pb_glossary] [pb_glossary id=\"3065\"]faults[\/pb_glossary] have side-to-side motion. [pb_glossary id=\"3076\"]Strike-slip[\/pb_glossary] [pb_glossary id=\"3065\"]faults[\/pb_glossary] are most commonly associated with [pb_glossary id=\"2601\"]transform[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries and are prevalent in [pb_glossary id=\"2601\"]transform[\/pb_glossary] [pb_glossary id=\"1934\"]fracture[\/pb_glossary] zones along [pb_glossary id=\"2630\"]mid-ocean ridges[\/pb_glossary]. In pure [pb_glossary id=\"3076\"]strike-slip[\/pb_glossary] motion, [pb_glossary id=\"3065\"]fault[\/pb_glossary] blocks on either side of the [pb_glossary id=\"3065\"]fault[\/pb_glossary] do not move up or down relative to each other, rather move laterally, side to side. The direction of [pb_glossary id=\"3076\"]strike-slip[\/pb_glossary] movement is determined by an observer standing on a block on one side of the [pb_glossary id=\"3065\"]fault[\/pb_glossary]. If the block on the opposing side of the [pb_glossary id=\"3065\"]fault[\/pb_glossary] moves left relative to the observer\u2019s block, this is called [pb_glossary id=\"2632\"]sinistral[\/pb_glossary] motion. If the opposing block moves right, it is [pb_glossary id=\"3077\"]dextral[\/pb_glossary] motion.\n\nVideo showing motion in a [pb_glossary id=\"3076\"]strike-slip[\/pb_glossary] [pb_glossary id=\"3065\"]fault[\/pb_glossary].\n\n&nbsp;\n\n[video width=\"1920\" height=\"1080\" mp4=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/strikeslip.mp4\"][\/video]\n\n[caption id=\"attachment_4312\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.5-Video-QR-Code.png\"><img class=\"size-thumbnail wp-image-624\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this interactive activity via this QR Code.[\/caption]\n\nBends along [pb_glossary id=\"3076\"]strike-slip[\/pb_glossary] [pb_glossary id=\"3065\"]faults[\/pb_glossary] create areas of [pb_glossary id=\"1446\"]compression[\/pb_glossary] or [pb_glossary id=\"1445\"]tension[\/pb_glossary] between the sliding blocks (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). [pb_glossary id=\"1445\"]Tensional[\/pb_glossary] [pb_glossary id=\"2915\"]stresses[\/pb_glossary] create transtensional features with normal [pb_glossary id=\"3065\"]faults[\/pb_glossary] and basins, such as the Salton Sea in California. [pb_glossary id=\"1446\"]Compressional[\/pb_glossary] [pb_glossary id=\"2915\"]stresses[\/pb_glossary] create [pb_glossary id=\"2634\"]transpressional[\/pb_glossary] features with [pb_glossary id=\"3073\"]reverse faults[\/pb_glossary] and cause small-scale mountain building, such as the San Gabriel Mountains in California. The [pb_glossary id=\"3065\"]faults[\/pb_glossary] that splay off [pb_glossary id=\"2634\"]transpression[\/pb_glossary] or [pb_glossary id=\"2635\"]transtension[\/pb_glossary] features are known as [pb_glossary id=\"3078\"]flower structures[\/pb_glossary].\n\n[caption id=\"attachment_3363\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.5_Flowerstructure1.png\"><img class=\"size-medium wp-image-625\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1-300x173.png\" alt=\"Block diagrams of mountains or basins in flower structures.\" width=\"300\" height=\"173\"><\/a> Flower structures created by strike-slip faults. Depending on the relative movement in relation to the bend in the fault, flower structures can create basins or mountains.[\/caption]\n\n<span style=\"font-weight: 400\">An example of a [pb_glossary id=\"3077\"]dextral[\/pb_glossary], [pb_glossary id=\"3077\"]right-lateral[\/pb_glossary] [pb_glossary id=\"3076\"]strike-slip[\/pb_glossary] [pb_glossary id=\"3065\"]fault[\/pb_glossary] is the San Andreas [pb_glossary id=\"3065\"]Fault[\/pb_glossary], which denotes a [pb_glossary id=\"2601\"]transform[\/pb_glossary] boundary between the North American and Pacific [pb_glossary id=\"2591\"]plates[\/pb_glossary]. An example of a [pb_glossary id=\"2632\"]sinistral[\/pb_glossary], [pb_glossary id=\"2632\"]left-lateral[\/pb_glossary] [pb_glossary id=\"3076\"]strike-slip[\/pb_glossary] [pb_glossary id=\"3065\"]fault[\/pb_glossary] is the Dead Sea [pb_glossary id=\"3065\"]fault[\/pb_glossary] in Jordan and Israel.<\/span>\n\n&nbsp;\n\nVideo showing how [pb_glossary id=\"3065\"]faults[\/pb_glossary] are classified.\n\n[caption id=\"attachment_4320\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Classification-of-Faults-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-626\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/qlk7IfYMufs[\/embed]\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"61\"]\n\n[caption id=\"attachment_4311\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.5-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-627\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.5 via this QR Code.[\/caption]\n<h2><strong>9.6 Earthquake Essentials<\/strong><\/h2>\n<span style=\"font-weight: 400\">Earthquakes are felt at the surface of the Earth when energy is released by blocks of rock sliding past each other, i.e. [pb_glossary id=\"3065\"]faulting[\/pb_glossary] has occurred. [pb_glossary id=\"3087\"]Seismic energy[\/pb_glossary] thus released travels through the Earth in the form of [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves. <\/span>Most earthquakes occur along active [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries. [pb_glossary id=\"1183\"]Intraplate[\/pb_glossary] earthquakes (not along [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries) occur and are still poorly understood. The\u00a0<a href=\"http:\/\/earthquake.usgs.gov\/earthquakes\/map\/#%7B%22feed%22%3A%227day_all%22%2C%22search%22%3Anull%2C%22listFormat%22%3A%22default%22%2C%22sort%22%3A%22newest%22%2C%22basemap%22%3A%22grayscale%22%2C%22autoUpdate%22%3Atrue%2C%22restrictListToMap%22%3Atrue%2C%22timeZone%22%3A%22utc%22%2C%22mapposition%22%3A%5B%5B32.93492866908233%2C-125.88134765625%5D%2C%5B47.97521412341618%2C-104.32617187499999%5D%5D%2C%22overlays%22%3A%7B%22plates%22%3Atrue%7D%2C%22viewModes%22%3A%7B%22map%22%3Atrue%2C%22list%22%3Atrue%2C%22settings%22%3Atrue%2C%22help%22%3Afalse%7D%7D\">USGS Earthquakes Hazards Program<\/a>\u00a0has a real time map showing the most recent earthquakes..\n<h3><b>9.6.1 How Earthquakes Happen<\/b><\/h3>\n[caption id=\"attachment_3364\" align=\"alignright\" width=\"425\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/elastic-deformation-and-rupture-1024x531-1.png\"><img class=\"wp-image-628\" title=\"Steven Earle\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1-300x156.png\" alt=\"Process of elastic rebound: a) Undeformed state, b) accumulation of elastic strain, and c) brittle failure and release of elastic strain.\" width=\"425\" height=\"220\"><\/a> Process of elastic rebound: a) Undeformed state, b) accumulation of elastic strain, and c) brittle failure and release of elastic strain.[\/caption]\n\nThe release of [pb_glossary id=\"3087\"]seismic energy[\/pb_glossary] is explained by the [pb_glossary id=\"3079\"]elastic rebound[\/pb_glossary] [pb_glossary id=\"2655\"]theory[\/pb_glossary]. When rock is [pb_glossary id=\"2916\"]strained[\/pb_glossary] to the point that it undergoes [pb_glossary id=\"1452\"]brittle deformation[\/pb_glossary], The place where the initial offsetting rupture takes place between the [pb_glossary id=\"3065\"]fault[\/pb_glossary] blocks is called the [pb_glossary id=\"3080\"]focus[\/pb_glossary]. This [pb_glossary id=\"3081\"]offset[\/pb_glossary] propagates along the [pb_glossary id=\"3065\"]fault[\/pb_glossary], which is known as the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane.\n\nThe [pb_glossary id=\"3065\"]fault[\/pb_glossary] blocks of persistent [pb_glossary id=\"3065\"]faults[\/pb_glossary] like the Wasatch [pb_glossary id=\"3065\"]Fault[\/pb_glossary] (Utah), that show recurring movements, are locked together by friction. Over hundreds to thousands of years, [pb_glossary id=\"2915\"]stress[\/pb_glossary] builds up along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] until it overcomes frictional resistance, rupturing the rock and initiating [pb_glossary id=\"3065\"]fault[\/pb_glossary] movement. The deformed unbroken rocks snap back toward their original shape in a process called [pb_glossary id=\"3079\"]elastic rebound[\/pb_glossary]<b>.<\/b> Think of bending a stick until it breaks; stored energy is released, and the broken pieces return to near their original orientation.\n\nBending, the [pb_glossary id=\"1450\"]ductile deformation[\/pb_glossary] of the rocks near a [pb_glossary id=\"3065\"]fault[\/pb_glossary], reflects a build-up of [pb_glossary id=\"2915\"]stress[\/pb_glossary]. In earthquake-prone areas like California, [pb_glossary id=\"2916\"]strain[\/pb_glossary] gauges are used to measure this bending and help seismologists, scientists who study earthquakes, understand more about predicting them. In locations where the [pb_glossary id=\"3065\"]fault[\/pb_glossary] is not locked, [pb_glossary id=\"3087\"]seismic[\/pb_glossary] [pb_glossary id=\"2915\"]stress[\/pb_glossary] causes continuous, gradual displacement between the [pb_glossary id=\"3065\"]fault[\/pb_glossary] blocks called [pb_glossary id=\"3065\"]fault[\/pb_glossary] [pb_glossary id=\"2447\"]creep[\/pb_glossary]. [pb_glossary id=\"3065\"]Fault[\/pb_glossary] [pb_glossary id=\"2447\"]creep[\/pb_glossary] occurs along some parts of the San Andreas [pb_glossary id=\"3065\"]Fault[\/pb_glossary] (California).\n\nAfter an initial earthquake, continuous application of [pb_glossary id=\"2915\"]stress[\/pb_glossary] in the [pb_glossary id=\"2580\"]crust[\/pb_glossary] causes elastic energy to begin to build again during a [pb_glossary id=\"2192\"]period[\/pb_glossary] of inactivity along the [pb_glossary id=\"3065\"]fault[\/pb_glossary]. The accumulating elastic [pb_glossary id=\"2916\"]strain[\/pb_glossary] may be periodically released to produce small earthquakes on or near the main [pb_glossary id=\"3065\"]fault[\/pb_glossary] called [pb_glossary id=\"3082\"]foreshocks[\/pb_glossary]. [pb_glossary id=\"3082\"]Foreshocks[\/pb_glossary] can occur hours or days before a large earthquake, or may not occur at all. The main release of energy during the major earthquake is known as the [pb_glossary id=\"3083\"]mainshock[\/pb_glossary]. [pb_glossary id=\"3084\"]Aftershocks[\/pb_glossary] may follow the [pb_glossary id=\"3083\"]mainshock[\/pb_glossary] to adjust new [pb_glossary id=\"2916\"]strain[\/pb_glossary] produced during the [pb_glossary id=\"3065\"]fault[\/pb_glossary] movement and generally decrease over time.\n<h3><b>9.6.2 Focus and Epicenter<\/b><\/h3>\n[caption id=\"attachment_3365\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Epicenter_Diagram.svg_.png\"><img class=\"wp-image-629 size-medium\" title=\"By Rostik252004 (Own work, based on File:Epicenter Diagram.svg) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Epicenter_Diagram.svg_-300x233.png\" alt=\"The hypocenter is the point from which seismic energy emanates. The epicenter is the point on land surface vertically above the hypocenter.\" width=\"300\" height=\"233\"><\/a> The hypocenter is the point along the fault plane in the subsurface from which seismic energy emanates. The epicenter is the point on land surface vertically above the hypocenter.[\/caption]\n<p style=\"text-align: left\">The earthquake [pb_glossary id=\"3080\"]focus[\/pb_glossary], also called\u00a0<strong>[pb_glossary id=\"3080\"]hypocenter[\/pb_glossary]<\/strong>, is the initial point of rupture and displacement of the rock moves from the [pb_glossary id=\"3080\"]hypocenter[\/pb_glossary] along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] surface. The earthquake [pb_glossary id=\"3080\"]focus[\/pb_glossary] or [pb_glossary id=\"3080\"]hypocenter[\/pb_glossary] is the point along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane from which initial [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves spread outward and is always at some depth below the ground surface. From the [pb_glossary id=\"3080\"]focus[\/pb_glossary], rock displacement propagates up, down, and laterally along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane. This displacement produces shock waves called [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves.\u00a0 The larger the displacement between the opposing [pb_glossary id=\"3065\"]fault[\/pb_glossary] blocks and the further the displacement propagates along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] surface, the more [pb_glossary id=\"3087\"]seismic energy[\/pb_glossary] is released and the greater the amount and time of shaking is produced. The [pb_glossary id=\"3085\"]epicenter[\/pb_glossary] is the location on the Earth\u2019s surface vertically above the [pb_glossary id=\"3080\"]focus[\/pb_glossary]. This is the location that most news reports give because it is the center of the area where people are affected.<\/p>\n\n<h3><b>9.6.3 Seismic Waves<\/b><\/h3>\nTo understand earthquakes and how earthquake energy moves through the Earth, consider the basic properties of waves. Waves describe how energy moves through a medium, such as rock or unconsolidated [pb_glossary id=\"2678\"]sediments[\/pb_glossary] in the case of earthquakes. Wave [pb_glossary id=\"3184\"]amplitude[\/pb_glossary] indicates the [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] or height of earthquake motion. [pb_glossary id=\"3186\"]Wavelength[\/pb_glossary] is the distance between two successive peaks of a wave. Wave frequency is the number of repetitions of the motion over a [pb_glossary id=\"2192\"]period[\/pb_glossary] of time, cycles per time unit. [pb_glossary id=\"2192\"]Period[\/pb_glossary], which is the amount of time for a wave to travel one [pb_glossary id=\"3186\"]wavelength[\/pb_glossary], is the inverse of frequency. When multiple waves combine, they can interfere with each other (see figure). When waves combine in sync, they produce constructive interference, where the influence of one wave adds to and magnifies the other. If waves are out of sync, they produce destructive interference, which diminishes the amplitudes of both waves. If two combined waves have the same [pb_glossary id=\"3184\"]amplitude[\/pb_glossary] and frequency but are one-half [pb_glossary id=\"3186\"]wavelength[\/pb_glossary] out of sync, the resulting destructive interference can eliminate each wave. These processes of wave [pb_glossary id=\"3184\"]amplitude[\/pb_glossary], frequency, [pb_glossary id=\"2192\"]period[\/pb_glossary], and constructive and destructive interference determine the [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] and intensity of earthquakes.\n\n[caption id=\"attachment_3366\" align=\"aligncenter\" width=\"690\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Waventerference.gif\"><img class=\"size-full wp-image-630\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Waventerference.gif\" alt=\"When two waves interact, they can increase or decrease each others amplitude depending on if they are aligned\" width=\"690\" height=\"295\"><\/a> Example of constructive and destructive interference; note red line representing the results of interference.[\/caption]\n\n[pb_glossary id=\"3087\"]Seismic[\/pb_glossary] waves are the physical expression of energy released by the [pb_glossary id=\"3079\"]elastic rebound[\/pb_glossary] of rock within displaced [pb_glossary id=\"3065\"]fault[\/pb_glossary] blocks and are felt as an earthquake. [pb_glossary id=\"3087\"]Seismic[\/pb_glossary] waves occur as [pb_glossary id=\"3088\"]body waves[\/pb_glossary] and [pb_glossary id=\"3089\"]surface waves[\/pb_glossary]. [pb_glossary id=\"3088\"]Body waves[\/pb_glossary] pass underground through the Earth\u2019s interior body and are the first [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves to propagate out from the [pb_glossary id=\"3080\"]focus[\/pb_glossary]. Body waves include primary (P) waves and secondary (S) waves. [pb_glossary id=\"3086\"]P waves[\/pb_glossary] are the fastest [pb_glossary id=\"3088\"]body waves[\/pb_glossary] and move through rock via [pb_glossary id=\"1446\"]compression[\/pb_glossary], very much like sound waves move through air. Rock particles move forward and back during passage of the [pb_glossary id=\"3086\"]P waves[\/pb_glossary], enabling them to travel through solids, liquids, plasma, and gases. [pb_glossary id=\"3090\"]S waves[\/pb_glossary] travel slower, following [pb_glossary id=\"3086\"]P waves[\/pb_glossary], and propagate as [pb_glossary id=\"1447\"]shear[\/pb_glossary] waves that move rock particles from side to side. Because they are restricted to lateral movement, [pb_glossary id=\"3090\"]S waves[\/pb_glossary] can only travel through solids but not liquids, plasma, or gases.\n\n<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Onde_compression_impulsion_1d_30_petit.gif\"><img class=\"wp-image-631 aligncenter\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Onde_compression_impulsion_1d_30_petit.gif\" alt=\"P-waves are compressional.\" width=\"461\" height=\"349\"><\/a>\n<p style=\"text-align: center\"><em><span style=\"font-size: 10pt\">P-waves are compressional<\/span>.<\/em><\/p>\n\n\n[caption id=\"attachment_3369\" align=\"aligncenter\" width=\"476\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Onde_cisaillement_impulsion_1d_30_petit.gif\"><img class=\"wp-image-632\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Onde_cisaillement_impulsion_1d_30_petit.gif\" alt=\"S waves are shear.\" width=\"476\" height=\"361\"><\/a> S waves are shear.[\/caption]\n\nDuring an earthquake, [pb_glossary id=\"3088\"]body waves[\/pb_glossary] pass through the Earth and into the [pb_glossary id=\"2586\"]mantle[\/pb_glossary] as a sub-spherical wave front. Considering a point on a wave front, the path followed by a specific point on the spreading wave front is called a [pb_glossary id=\"3087\"]seismic[\/pb_glossary] ray and a [pb_glossary id=\"3087\"]seismic[\/pb_glossary] ray reaches a specific [pb_glossary id=\"3095\"]seismograph[\/pb_glossary] located at one of thousands of [pb_glossary id=\"3087\"]seismic[\/pb_glossary] monitoring stations scattered over the Earth. D<span style=\"font-weight: 400\">ensity increases with depth in the Earth, and since [pb_glossary id=\"3087\"]seismic[\/pb_glossary] velocity increases with density, a process called <\/span><b>[pb_glossary id=\"3091\"]refraction[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> causes earthquake rays to curve away from the vertical and bend back toward the surface, passing through different bodies of rock along the way.<\/span>\n\n[pb_glossary id=\"3089\"]Surface waves[\/pb_glossary] are produced when [pb_glossary id=\"3088\"]body waves[\/pb_glossary] from the [pb_glossary id=\"3080\"]focus[\/pb_glossary] [pb_glossary id=\"1453\"]strike[\/pb_glossary] the Earth\u2019s surface. Surface waves travel along the Earth's surface, radiating outward from the [pb_glossary id=\"3085\"]epicenter[\/pb_glossary].\u00a0 [pb_glossary id=\"3089\"]Surface waves[\/pb_glossary] take the form of rolling waves called <a href=\"https:\/\/www.youtube.com\/watch?v=6yXgfYHAS7c\">Raleigh Waves<\/a> and side to side waves called <a href=\"https:\/\/www.youtube.com\/watch?v=t7wJu0Kts7w\">Love Waves<\/a> (watch videos for wave propagation animations). [pb_glossary id=\"3089\"]Surface waves[\/pb_glossary] are produced primarily as the more energetic [pb_glossary id=\"3090\"]S waves[\/pb_glossary] [pb_glossary id=\"1453\"]strike[\/pb_glossary] the surface from below with some [pb_glossary id=\"3089\"]surface wave[\/pb_glossary] energy contributed by [pb_glossary id=\"3086\"]P waves[\/pb_glossary] (videos courtesy <a href=\"http:\/\/blog.Wolfram.com\">blog.Wolfram.com<\/a>). [pb_glossary id=\"3089\"]Surface waves[\/pb_glossary] travel more slowly than [pb_glossary id=\"3088\"]body waves[\/pb_glossary] and because of their complex horizontal and vertical movement, [pb_glossary id=\"3089\"]surface waves[\/pb_glossary] are responsible for most of the damage caused by an earthquake. [pb_glossary id=\"3092\"]Love waves[\/pb_glossary] produce predominantly horizontal ground shaking and, ironically from their name, are the most destructive. [pb_glossary id=\"3093\"]Rayleigh waves[\/pb_glossary] produce an elliptical motion with longitudinal dilation and [pb_glossary id=\"1446\"]compression[\/pb_glossary], like ocean waves. However, Raleigh waves cause rock particles to move in a direction opposite to that of water particles in ocean waves.\n\nThe Earth has been described as ringing like a bell after an earthquake with earthquake energy reverberating inside it.\u00a0 Like other waves, [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves refract (bend) and bounce (reflect) when passing through rocks of differing densities.\u00a0 [pb_glossary id=\"3090\"]S waves[\/pb_glossary], which cannot move through liquid, are blocked by the Earth's liquid [pb_glossary id=\"2595\"]outer core[\/pb_glossary], creating an S wave shadow zone on the side of the planet opposite to the earthquake [pb_glossary id=\"3080\"]focus[\/pb_glossary]. [pb_glossary id=\"3086\"]P waves[\/pb_glossary], on the other hand, pass through the [pb_glossary id=\"2589\"]core[\/pb_glossary], but are refracted into the [pb_glossary id=\"2589\"]core[\/pb_glossary] by the difference of density at the [pb_glossary id=\"2589\"]core[\/pb_glossary]-[pb_glossary id=\"2586\"]mantle[\/pb_glossary] boundary. This has the effect of creating a cone shaped [pb_glossary id=\"3086\"]P wave[\/pb_glossary] shadow zone on parts of the other side of the Earth from the [pb_glossary id=\"3080\"]focus[\/pb_glossary].\n\n[embed]https:\/\/player.vimeo.com\/video\/153300296[\/embed]\n<p style=\"text-align: center\"><span style=\"font-size: 10pt\"><em><a href=\"https:\/\/vimeo.com\/153300296\">2011 Tohoku Earthquake, Mag. 9.0. Body and Surface Waves<\/a> from <a href=\"https:\/\/vimeo.com\/seismicsoundlab\">seismicsoundlab<\/a> on <a href=\"https:\/\/vimeo.com\">Vimeo<\/a>.<\/em><\/span><\/p>\n\n\n[caption id=\"attachment_4292\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/2011-Tohoku-Earthquake-Vimeo-QR-Code.png\"><img class=\"size-thumbnail wp-image-633\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this Vimeo video via this QR Code.[\/caption]\n<h3>9.6.4 Induced Seismicity<\/h3>\n[caption id=\"attachment_2493\" align=\"alignleft\" width=\"334\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Cumulative_induced_seismicity.png\"><img class=\"wp-image-61\" title=\"USGS, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-300x228.png\" alt=\"There is a large spike in earthquakes\" width=\"334\" height=\"254\"><\/a> Frequency of earthquakes in the central United States. Note the sharp increase in the number of earthquakes from 2010 to 2015.[\/caption]\n\nEarthquakes known as [pb_glossary id=\"3109\"]induced seismicity[\/pb_glossary] occur near [pb_glossary id=\"3339\"]natural gas[\/pb_glossary] extraction sites because of human activity. Injection of waste fluids in the ground, commonly a byproduct of an extraction process for [pb_glossary id=\"3339\"]natural gas[\/pb_glossary] known as <strong>[pb_glossary id=\"3108\"]fracking[\/pb_glossary]<\/strong>, can increase the outward pressure that liquid in the [pb_glossary id=\"3116\"]pores[\/pb_glossary] of a rock exerts, known as [pb_glossary id=\"3116\"]pore[\/pb_glossary] pressure.\u00a0 The increase in [pb_glossary id=\"3116\"]pore[\/pb_glossary] pressure decreases the frictional forces that keep rocks from sliding past each other, essentially lubricating [pb_glossary id=\"3065\"]fault[\/pb_glossary] planes. <span style=\"font-weight: 400\">This effect is causing earthquakes to occur near injection sites, in a human induced activity known as <\/span><b>[pb_glossary id=\"3109\"]induced seismicity[\/pb_glossary]<\/b><span style=\"font-weight: 400\">. \u00a0<\/span>The significant increase in drilling activity in the central United States has spurred the requirement for the disposal of significant amounts of waste drilling fluid, resulting in a measurable change in the cumulative number of earthquakes experienced in the region.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"62\"]\n\n[caption id=\"attachment_4313\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.6-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-634\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.6 via this QR Code.[\/caption]\n<h2><strong>9.7 Measuring Earthquakes<\/strong><\/h2>\n<h3><b>9.7.1 Seismographs<\/b><\/h3>\n[caption id=\"attachment_3371\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.5-seismograph-horiz.gif\"><img class=\"wp-image-635 size-medium\" title=\"Source: IRIS https:\/\/www.iris.edu\/hq\/inclass\/animation\/seismograph_horizontal See website for usage rights.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph-horiz-300x225.gif\" alt=\"Animation depicts a seismograph consisting of swinging-gate pendulum with a pencil on the end that shakes back and forth when encountering seismic wave.\" width=\"300\" height=\"225\"><\/a> Animation of a horizontal seismograph.[\/caption]\n\nPeople feel approximately 1 million earthquakes a year, usually when they are close to the source and the earthquake registers at least [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 2.5. Major earthquakes of [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 7.0 and higher are extremely rare. The U. S. Geological Survey (USGS) Earthquakes Hazards Program <a href=\"http:\/\/earthquake.usgs.gov\/earthquakes\/map\/#%7B%22feed%22%3A%227day_all%22%2C%22search%22%3Anull%2C%22listFormat%22%3A%22default%22%2C%22sort%22%3A%22newest%22%2C%22basemap%22%3A%22grayscale%22%2C%22autoUpdate%22%3Atrue%2C%22restrictListToMap%22%3Atrue%2C%22timeZone%22%3A%22utc%22%2C%22mapposition%22%3A%5B%5B32.93492866908233%2C-125.88134765625%5D%2C%5B47.97521412341618%2C-104.32617187499999%5D%5D%2C%22overlays%22%3A%7B%22plates%22%3Atrue%7D%2C%22viewModes%22%3A%7B%22map%22%3Atrue%2C%22list%22%3Atrue%2C%22settings%22%3Atrue%2C%22help%22%3Afalse%7D%7D\">real-time map<\/a> shows the location and [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] of recent earthquakes around the world.\n\nTo accurately study [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves, geologists use <strong>[pb_glossary id=\"3095\"]seismographs[\/pb_glossary]<\/strong> that can measure even the slightest ground vibrations. Early 20<sup>th<\/sup>-century seismograms use a weighted pen (pendulum) suspended by a long [pb_glossary id=\"3174\"]spring[\/pb_glossary] above a recording device fixed solidly to the ground. The recording device is a rotating drum mounted with a continuous strip of paper. During an earthquake, the suspended pen stays motionless and records ground movement on the paper strip. The resulting graph a seismogram. Digital versions use magnets, wire coils, electrical sensors, and digital signals instead of mechanical pens, springs, drums, and paper. A [pb_glossary id=\"3095\"]seismograph[\/pb_glossary] array is multiple [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] configured to measure vibrations in three directions: north-south (x [pb_glossary id=\"1456\"]axis[\/pb_glossary]), east-west (y [pb_glossary id=\"1456\"]axis[\/pb_glossary]), and up-down (z [pb_glossary id=\"1456\"]axis[\/pb_glossary]).\n\n&nbsp;\n\n[caption id=\"attachment_3372\" align=\"aligncenter\" width=\"600\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.5-seismograph_vert.gif\"><img class=\"wp-image-636 size-full\" title=\"Source: IRIS https:\/\/www.iris.edu\/hq\/inclass\/animation\/seismograph_vertical See website for usage rights.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph_vert.gif\" alt=\"Depicts a vertical seismograph, and earthquake waves traveling past the device. The device consist of a rotating recording drum, where a mass and pencil on a spring bounce vertically when earthquake waves pass trough them.\" width=\"600\" height=\"450\"><\/a> Animation of how a basic vertical seismograph records seismic waves.[\/caption]\n\n[caption id=\"attachment_3374\" align=\"aligncenter\" width=\"1094\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.7-Seismogram.png\"><img class=\"wp-image-637 size-full\" title=\"Made by Paul Inkenbrandt using example data from IRIS.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram.png\" alt=\"Squiggly lines along a horizontal axis. When the P-wave arrives, a small amplitude squiggle shows up. Then the S-wave arrives, and another small-amplitude squiggle shows. Finally, the surface-waves arrive, and large-amplitude waves show up, two to three times the amplitude of the body waves. Then the wave taper off and the line becomes essentially horizontal again.\" width=\"1094\" height=\"398\"><\/a> A seismogram showing the arrivals of the P, S, and surface waves[\/caption]\n\nTo pinpoint the location of an earthquake [pb_glossary id=\"3085\"]epicenter[\/pb_glossary], seismologists use the differences in arrival times of the P, S, and [pb_glossary id=\"3089\"]surface waves[\/pb_glossary]. After an earthquake, [pb_glossary id=\"3086\"]P waves[\/pb_glossary] will appear first on a seismogram, followed by [pb_glossary id=\"3090\"]S waves[\/pb_glossary], and finally [pb_glossary id=\"3089\"]surface waves[\/pb_glossary], which have the largest [pb_glossary id=\"3184\"]amplitude[\/pb_glossary]. It is important to note that [pb_glossary id=\"3089\"]surface waves[\/pb_glossary] lose energy quickly, so they are not measurable at great distances from the [pb_glossary id=\"3085\"]epicenter[\/pb_glossary]. These time differences determine the distance but not the direction of the epicenter. By using wave arrival times recorded on [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] at multiple stations, seismologists can apply triangulation to pin point the location of the [pb_glossary id=\"3085\"]epicenter[\/pb_glossary] of an earthquake. At least three seismograph stations are needed for triangulation. The distance from each station to the [pb_glossary id=\"3085\"]epicenter[\/pb_glossary] is plotted as the radius of a circle. The epicenter is demarked where the circles intersect. This method also works in 3D, using multi-[pb_glossary id=\"1456\"]axis[\/pb_glossary] seismographs and sphere radii to calculate the underground depth of the [pb_glossary id=\"3080\"]focus[\/pb_glossary].\n<p style=\"text-align: left\">This video shows the method of triangulation to locate the [pb_glossary id=\"3085\"]epicenter[\/pb_glossary] of an earthquake.<\/p>\n\n\n[caption id=\"attachment_4295\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-638\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/oBS7BKqHRhs[\/embed]\n<h3><b>9.7.2 Seismograph Network<\/b><\/h3>\n[caption id=\"attachment_3375\" align=\"aligncenter\" width=\"483\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/GSN_topo_20March2017.jpg\"><img class=\"wp-image-639\" title=\"http:\/\/www.iris.edu\/hq\/programs\/gsn\/maps\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/GSN_topo_20March2017-300x183.jpg\" alt=\"World map of a global network of seismic stations. The map shows that seismic stations are widespread and there are many on every continent.\" width=\"483\" height=\"295\"><\/a> Global network of seismic stations. Note that this map does not show all of the world's seismic stations, just one of the networks of stations scientists use to measure seismic activity.[\/caption]\n<p style=\"text-align: left\"><span style=\"font-weight: 400\">The <\/span><a href=\"http:\/\/www.isc.ac.uk\/registries\/\"><span style=\"font-weight: 400\">International Registry of Seismograph Stations<\/span><\/a><span style=\"font-weight: 400\"> lists more than 20,000 [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] on the planet.\u00a0<\/span>By comparing data from multiple [pb_glossary id=\"3095\"]seismographs[\/pb_glossary], scientists can map the properties of the inside of the Earth, detect detonations of large explosive devices, and predict [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary]. The <a href=\"https:\/\/earthquake.usgs.gov\/monitoring\/gsn\/\">Global Seismic Network<\/a>, a worldwide set of linked [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] that electronically distribute real-time data, includes more than 150 stations that meet specific design and precision standards. The <a href=\"http:\/\/www.usarray.org\/\">USArray<\/a> is a network of hundreds of permanent and transportable [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] in the United States that are used to map the subsurface activity of earthquakes (see video).<\/p>\nAlong with monitoring for earthquakes and related hazards, the Global [pb_glossary id=\"3095\"]Seismograph[\/pb_glossary] Network helps detect nuclear weapons testing, which is monitored by the <a href=\"https:\/\/www.ctbto.org\/\">Comprehensive Nuclear Test Ban Treaty Organization<\/a>.\u00a0 Most recently, [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] have been used to determine nuclear weapons testing by North Korea.\n\n[caption id=\"attachment_4302\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Nepal-Earthquake-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-640\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/5xc-rNOISQE[\/embed]\n<p style=\"text-align: center\"><span style=\"font-size: 10pt\"><em>Nepal Earthquake M7.9 Ground Motion Visualization<\/em><\/span><\/p>\n\n<h3><b>9.7.3 Seismic tomography<\/b><\/h3>\n<span style=\"font-weight: 400\">Very much like a CT (Computed [pb_glossary id=\"3096\"]Tomography[\/pb_glossary]) scan uses X-rays at different angles to image the inside of a body, <\/span><b>[pb_glossary id=\"3087\"]seismic[\/pb_glossary] [pb_glossary id=\"3096\"]tomography[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> uses [pb_glossary id=\"3087\"]seismic[\/pb_glossary] rays from thousands of earthquakes that occur each year, <\/span>passing at all angles through masses of rock, to generate images of internal Earth structures.\n\n[caption id=\"attachment_3376\" align=\"alignright\" width=\"480\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Speeds_of_seismic_waves.png\"><img class=\"wp-image-641\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-300x205.png\" alt=\"Speed of seismic waves with depth in the earth. Two thousand kilometers is 1240 miles.\" width=\"480\" height=\"327\"><\/a> Speed of seismic waves with depth in the earth. Two thousand kilometers is 1240 miles.[\/caption]\n\n&nbsp;\n\n<span style=\"font-weight: 400\">Using the assumption that the earth consists of homogenous layers, geologists developed a model of expected properties of earth materials at every depth within the earth called the PREM (Preliminary Reference Earth Model). These properties include [pb_glossary id=\"3087\"]seismic wave[\/pb_glossary] transmission velocity, which is dependent on rock density and elasticity. In the [pb_glossary id=\"2586\"]mantle[\/pb_glossary], [pb_glossary id=\"2689\"]temperature[\/pb_glossary] differences affect rock density. Cooler rocks have a higher density and therefore transmit [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves faster. <\/span><span style=\"font-weight: 400\">Warmer rocks have a lower density and transmit earthquake waves slower.\u00a0 When the arrival times of [pb_glossary id=\"3087\"]seismic[\/pb_glossary] rays at individual seismic stations are compared to arrival times predicted by PREM, differences are called\u00a0 <\/span><b>[pb_glossary id=\"3097\"]seismic anomalies[\/pb_glossary] <\/b><span style=\"font-weight: 400\">and can be measured for bodies of rock within the earth from\u00a0 seismic rays passing through them at stations of the [pb_glossary id=\"3087\"]seismic[\/pb_glossary] network.\u00a0 Because [pb_glossary id=\"3087\"]seismic[\/pb_glossary] rays travel at all angles from lots of earthquakes and arrive at lots of stations of the [pb_glossary id=\"3087\"]seismic[\/pb_glossary] network, like CT scans of the body, variations in the properties of the rock bodies allow 3D images to be constructed of the rock bodies through which the rays passed. Seismologists are thus able to construct 3D images of the interior of the Earth..<\/span>\n\n<span style=\"font-weight: 400\">For example, seismologists have mapped the Farallon [pb_glossary id=\"2591\"]Plate[\/pb_glossary], a [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] that [pb_glossary id=\"2602\"]subducted[\/pb_glossary] beneath North America during the last several million years, and the Yellowstone [pb_glossary id=\"1185\"]magma chamber[\/pb_glossary], which is a product of the Yellowstone [pb_glossary id=\"2638\"]hot spot[\/pb_glossary] under the North American [pb_glossary id=\"2575\"]continent[\/pb_glossary]. Peculiarities of the Farallon [pb_glossary id=\"2591\"]Plate[\/pb_glossary] [pb_glossary id=\"2602\"]subduction[\/pb_glossary] are thought to be responsible for many features of western North America including the Rocky Mountains <\/span><span style=\"font-weight: 400\">(<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/8-earth-history\/\">See chapter 8<\/a>)<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3377\" align=\"aligncenter\" width=\"425\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/New_Plume.jpg\"><img class=\"wp-image-642\" title=\"From: http:\/\/www.uusatrg.utah.edu\/\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/New_Plume-300x222.jpg\" alt=\"Seismic tomograph showing the magma chamber beneath Yellowstone National Park\" width=\"425\" height=\"315\"><\/a> Seismic tomograph showing the magma chamber beneath Yellowstone National Park.[\/caption]\n\n[caption id=\"attachment_3378\" align=\"aligncenter\" width=\"358\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Farallon_Plate-e1490562202658.jpg\"><img class=\"wp-image-643\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Farallon_Plate-e1490562202658-300x276.jpg\" alt=\"Tomographic image of the Farallon plate in the mantle.\" width=\"358\" height=\"330\"><\/a> Tomographic image of the Farallon plate in the mantle below North America.[\/caption]\n<h3><b>9.7.4 Earthquake Magnitude and Intensity<\/b><\/h3>\n<h4><em>9.7.4.1 RICHTER SCALE<\/em><\/h4>\n<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"3098\"]Magnitude[\/pb_glossary]<\/strong> is the measure of the energy released by an earthquake. The <strong>[pb_glossary id=\"3099\"]Richter scale[\/pb_glossary]<\/strong> (M<sub>L<\/sub>), the first and most well-known [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] scale, was developed by Charles F. Richter (1900-1985) at the California Institute of Technology. This was the [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] scale used historically by early seismologists. <\/span>Used by early seismologists, [pb_glossary id=\"3099\"]Richter magnitude[\/pb_glossary] (M<sub>L<\/sub>) is determined from the maximum [pb_glossary id=\"3184\"]amplitude[\/pb_glossary] of the pen tracing on the seismogram recording. Adjustments for [pb_glossary id=\"3085\"]epicenter[\/pb_glossary] distance from the [pb_glossary id=\"3095\"]seismograph[\/pb_glossary] are made using the arrival-time differences of S and [pb_glossary id=\"3086\"]P waves[\/pb_glossary].\n\n<span style=\"font-weight: 400\">The [pb_glossary id=\"3099\"]Richter Scale[\/pb_glossary] is logarithmic, based on powers of 10. This means an increase of one Richter unit represents a 10-fold increase in [pb_glossary id=\"3087\"]seismic[\/pb_glossary]-wave [pb_glossary id=\"3184\"]amplitude[\/pb_glossary] or in other words, a\u00a0[pb_glossary id=\"3098\"]magnitude[\/pb_glossary] 6 earthquake shakes the ground 10 times more than a [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] 5. However, the <em>actual energy released<\/em> for each [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] unit is 32 times greater, which means a [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] 6 earthquake releases 32 times more energy than a [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] 5. <\/span>\n\n<span style=\"font-weight: 400\">The [pb_glossary id=\"3099\"]Richter Scale[\/pb_glossary] was developed for earthquakes in Southern California, using local [pb_glossary id=\"3095\"]seismographs[\/pb_glossary]. It has limited applications for larger distances and very large earthquakes. Therefore, most agencies no longer use the [pb_glossary id=\"3099\"]Richter Scale[\/pb_glossary]. [pb_glossary id=\"3100\"]Moment magnitude[\/pb_glossary] (M<sub>W<\/sub>), which is measured using [pb_glossary id=\"3087\"]seismic[\/pb_glossary] arrays and generates values comparable to the [pb_glossary id=\"3099\"]Richter Scale[\/pb_glossary], is more accurate for measuring earthquakes across the Earth, including large earthquakes, although they require more time to calculate. News media often report Richter magnitudes right after an earthquake occurs even though scientific calculations now use moment magnitudes.<\/span>\n<h4><em><b>9.7.4.2 MOMENT MAGNITUDE SCALE<\/b><\/em><\/h4>\n<span style=\"font-weight: 400\">The <strong>[pb_glossary id=\"3100\"]Moment Magnitude[\/pb_glossary] scale<\/strong> depicts the absolute size of earthquakes, comparing information from multiple locations and using a measurement of actual energy released calculated from cross-sectional area of rupture, amount of slippage, and the rigidity of the rocks. Because each earthquake occurs in a unique geologic setting and the rupture area is often hard to measure, estimates of [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] can take days or even months to calculate. <\/span>\n\n<span style=\"font-weight: 400\">Like the [pb_glossary id=\"3099\"]Richter Scale[\/pb_glossary], the [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] scale is logarithmic. [pb_glossary id=\"3098\"]Magnitude[\/pb_glossary] values of the two scales are approximately equal, except for very large earthquakes. Both scales are used for reporting earthquake [pb_glossary id=\"3098\"]magnitude[\/pb_glossary]. The [pb_glossary id=\"3099\"]Richter Scale[\/pb_glossary] provides a quick [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] estimate immediately following the quake and thus, is usually reported in news accounts. [pb_glossary id=\"3100\"]Moment magnitude[\/pb_glossary] calculations take much longer but are more accurate and thus, more useful for scientific analysis. <\/span>\n\n[caption id=\"attachment_4301\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Moment-Magnitude-Explained-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-644\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/HL3KGK5eqaw[\/embed]\n<h4><em><b>9.7.4.3 Modified Mercalli Intensity Scale<\/b><\/em><\/h4>\n<span style=\"font-weight: 400\">The <strong>[pb_glossary id=\"3101\"]Modified Mercalli Intensity Scale[\/pb_glossary] (MMI) <\/strong><\/span>is a [pb_glossary id=\"2647\"]qualitative[\/pb_glossary] rating of ground-shaking intensity based on observable structural damage and people\u2019s perceptions. This scale uses a <span style=\"font-style: normal !msorm\"><em>I<\/em><\/span> (Roman numeral one) rating for the lowest intensity and <span style=\"font-style: normal !msorm\"><em>X<\/em><\/span> (ten) for the highest (see table) and can vary depending on [pb_glossary id=\"3085\"]epicenter[\/pb_glossary] location and population density, such as urban versus rural settings. Historically, scientists used the MMI Scale to categorize earthquakes before they developed [pb_glossary id=\"2646\"]quantitative[\/pb_glossary] measurements of [pb_glossary id=\"3098\"]magnitude[\/pb_glossary]. Intensity maps show locations of the most severe damage, based on residential questionnaires, local news articles, and on-site assessment reports.\n<table style=\"width: 111.56%;height: 868px\">\n<thead>\n<tr style=\"height: 28px\">\n<th style=\"width: 11.7105%;text-align: center;height: 28px\">Intensity<\/th>\n<th style=\"width: 13.8101%;text-align: center;height: 28px\">Shaking<\/th>\n<th style=\"width: 74.3478%;height: 28px\">Description\/Damage<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr style=\"height: 28px\">\n<td style=\"background-color: #ffffff;width: 11.7105%;text-align: center;vertical-align: middle;height: 28px\">I<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 28px\">Not felt<\/td>\n<td style=\"width: 74.3478%;height: 28px\">Not felt except by a very few under especially favorable conditions.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #dfe6fe;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">II<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Weak<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Felt only by a few persons at rest,especially on upper floors of buildings.<\/td>\n<\/tr>\n<tr style=\"height: 140px\">\n<td style=\"background-color: #82f9fb;width: 11.7105%;text-align: center;vertical-align: middle;height: 140px\">III<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 140px\">Weak<\/td>\n<td style=\"width: 74.3478%;height: 140px\">Felt quite noticeably by persons indoors, especially on upper floors of buildings.\nMany people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.<\/td>\n<\/tr>\n<tr style=\"height: 140px\">\n<td style=\"background-color: #7efbdf;width: 11.7105%;text-align: center;vertical-align: middle;height: 140px\">IV<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 140px\">Light<\/td>\n<td style=\"width: 74.3478%;height: 140px\">Felt indoors by many, outdoors by few during the day. At night, some awakened.\nDishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #95f879;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">V<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Moderate<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #f7f835;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">VI<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Strong<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.<\/td>\n<\/tr>\n<tr style=\"height: 112px\">\n<td style=\"background-color: #fdca2c;width: 11.7105%;text-align: center;vertical-align: middle;height: 112px\">VII<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 112px\">Very strong<\/td>\n<td style=\"width: 74.3478%;height: 112px\">Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.<\/td>\n<\/tr>\n<tr style=\"height: 112px\">\n<td style=\"background-color: #ff701f;width: 11.7105%;text-align: center;vertical-align: middle;height: 112px\">VIII<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 112px\">Severe<\/td>\n<td style=\"width: 74.3478%;height: 112px\">Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.<\/td>\n<\/tr>\n<tr style=\"height: 84px\">\n<td style=\"background-color: #ec2516;width: 11.7105%;text-align: center;vertical-align: middle;height: 84px\">IX<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 84px\">Violent<\/td>\n<td style=\"width: 74.3478%;height: 84px\">Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #c81e11;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">X<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Extreme<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<a href=\"https:\/\/earthquake.usgs.gov\/learn\/topics\/mercalli.php\"><i><span style=\"font-weight: 400\">Table. Abridged Mercalli Scale from USGS General Interest Publication 1989-288-913.<\/span><\/i><\/a>\n<h4><em><b>9.7.4.4 Shake Maps<\/b><\/em><\/h4>\n[caption id=\"attachment_3379\" align=\"aligncenter\" width=\"408\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/shakemapintensity-e1490409875228.jpg\"><img class=\"wp-image-645\" title=\"https:\/\/earthquake.usgs.gov\/earthquakes\/eventpage\/nc17204#shakemap\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/shakemapintensity-e1490409875228-273x300.jpg\" alt=\"Example of a shake map.\" width=\"408\" height=\"449\"><\/a> Example of a shake map.[\/caption]\n\nShake maps, written ShakeMaps by the USGS, use high-quality, computer-interpolated data from [pb_glossary id=\"3095\"]seismograph[\/pb_glossary]\u00a0networks to show areas of intense shaking. Shake maps are useful in the crucial minutes after an earthquake, as they show emergency personnel where the greatest damage likely occurred and help them locate possibly damaged gas lines and other utility facilities.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"63\"]\n\n[caption id=\"attachment_4247\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-588\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.7 via this QR Code.[\/caption]\n<h2><strong>9.8 Earthquake Risk<\/strong><\/h2>\n<h3><b>9.8.1<\/b>\u00a0 \u00a0Factors that Determine Shaking<\/h3>\nEarthquake [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] is an absolute value that measures pure energy release. Intensity however, i.e. how much the ground shakes, is a determined by several factors.<b><\/b><b><\/b>\n\n<strong>Earthquake <\/strong><strong>[pb_glossary id=\"3098\"]Magnitude[\/pb_glossary]<\/strong><strong>\u2014<\/strong>In general, the larger the [pb_glossary id=\"3098\"]magnitude[\/pb_glossary], the stronger the shaking and the longer the shaking will last.\n\n<span style=\"font-weight: 400\">This table is taken from from the <a href=\"https:\/\/earthquake.usgs.gov\/learn\/topics\/mag_vs_int.php\">USGS<\/a> and shows scales of [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] and [pb_glossary id=\"3101\"]Mercalli[\/pb_glossary] Intensity, and descriptions of shaking and resulting damage.<\/span>\n<table style=\"width: 762px\">\n<tbody>\n<tr>\n<td style=\"width: 88px\"><b>[pb_glossary id=\"3098\"]Magnitude[\/pb_glossary]<\/b><\/td>\n<td style=\"text-align: center;width: 103px\"><b>[pb_glossary id=\"3101\"]Modified Mercalli Intensity[\/pb_glossary]<\/b><\/td>\n<td style=\"width: 528px\"><b>Shaking\/Damage Description<\/b><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>1.0 - 3.0<\/b><\/td>\n<td style=\"width: 103px;background-color: #69fad3;text-align: center;vertical-align: middle\"><b>I<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Only felt by a very few. <\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>3.0 - 3.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #82f056;text-align: center;vertical-align: middle\"><b>II - III<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Noticeable indoors, especially on upper floors.<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>4.0 - 4.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #eaf03c;text-align: center;vertical-align: middle\"><b>IV - V<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Most to all feel it. Dishes, doors, cars shake and possibly break.<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>5.0 - 5.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #edac3b;text-align: center;vertical-align: middle\"><b>VI - VII<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Everyone feels it. Some items knocked over or broken. Building damage possible.<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>6.0 - 6.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #eb5c15;text-align: center;vertical-align: middle\"><b>VII - IX<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Frightening amounts of shaking. Significant damage especially with poorly constructed buildings<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>\u2265 7.0<\/b><\/td>\n<td style=\"width: 103px;background-color: #f70202;text-align: center;vertical-align: middle\"><b>\u2265 VIII<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Significant destruction of buildings. Potential for objects to be thrown in air from shaking.<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h4><span style=\"font-weight: 400\">\u00a0<\/span><\/h4>\n<strong>Location and Direction\u2014<\/strong>Shaking is more severe closer to the [pb_glossary id=\"3085\"]epicenter[\/pb_glossary]. The severity of shaking is influenced by the location of the observer relative to [pb_glossary id=\"3085\"]epicenter[\/pb_glossary], direction of rupture propagation, and path of greatest rupture.\n\n<strong>Local Geologic Conditions<\/strong><strong>\u2014<\/strong>[pb_glossary id=\"3087\"]Seismic[\/pb_glossary] waves are affected by the nature of the ground materials through which they pass. Different materials respond differently to an earthquake. Think of shaking a block of Jello versus a meatloaf, one will jiggle much more when hit by waves of the same [pb_glossary id=\"3184\"]amplitude[\/pb_glossary]. The ground\u2019s response to shaking depends on the degree of substrate consolidation. Solid sedimentary, [pb_glossary id=\"2675\"]igneous[\/pb_glossary], or [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] [pb_glossary id=\"1971\"]bedrock[\/pb_glossary] shakes less than unconsolidated [pb_glossary id=\"2678\"]sediments[\/pb_glossary].\n\nThis video shows how different substrates behave in response to different [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves and their potential for destruction.\n\n&nbsp;\n\n[caption id=\"attachment_4293\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Amplification-and-Liquefaction-Youtube-QR-Code.png\"><img class=\"wp-image-646 size-thumbnail\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/536xSZ_XkSs[\/embed]\n\n[pb_glossary id=\"3087\"]Seismic[\/pb_glossary] waves move fastest through consolidated [pb_glossary id=\"1971\"]bedrock[\/pb_glossary], slower through unconsolidated [pb_glossary id=\"2678\"]sediments[\/pb_glossary], and slowest through unconsolidated [pb_glossary id=\"2678\"]sediments[\/pb_glossary] with a high water content. Seismic energy is transmitted by [pb_glossary id=\"3187\"]wave velocity[\/pb_glossary] and [pb_glossary id=\"3184\"]amplitude[\/pb_glossary]. When seismic waves slow down, energy is transferred to the [pb_glossary id=\"3184\"]amplitude[\/pb_glossary], increasing the motion of [pb_glossary id=\"3089\"]surface waves[\/pb_glossary], which in turn amplifies ground shaking.\n\n<strong>[pb_glossary id=\"3080\"]Focus[\/pb_glossary] depth<i style=\"font-size: 16px;font-weight: 400\">\u2014<\/i><\/strong>Deeper earthquakes cause less surface shaking because much of their energy, transmitted as [pb_glossary id=\"3088\"]body waves[\/pb_glossary], is lost before reaching the surface. Recall that [pb_glossary id=\"3089\"]surface waves[\/pb_glossary] are generated by P and [pb_glossary id=\"3090\"]S waves[\/pb_glossary] impacting the Earth\u2019s surface.\n<h3><b>9.8.2<\/b>\u00a0 \u00a0Factors that Determine Destruction<\/h3>\nJust as certain conditions will impact intensity of ground-shaking, several factors affect how much destruction is caused.\n\n[caption id=\"attachment_3380\" align=\"alignright\" width=\"347\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake.jpg\"><img class=\"wp-image-647\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake-300x199.jpg\" alt=\"Example of devastation on unreinforced masonry by seismic motion.\" width=\"347\" height=\"230\"><\/a> Example of devastation on unreinforced masonry by seismic motion.[\/caption]\n\n&nbsp;\n\n<strong>Building Materials\u2014<\/strong><span style=\"font-weight: 400\">The flexibility of a building material determines its resistance to earthquake damage. Unreinforced masonry (URM) is the material most devastated by ground shaking. Wood framing fastened with nails bends and flexes during [pb_glossary id=\"3087\"]seismic wave[\/pb_glossary] passage and is more likely to survive intact. Steel also has the ability to deform elastically before [pb_glossary id=\"2583\"]brittle[\/pb_glossary] failure. The <a href=\"http:\/\/www.bereadyslc.com\/fix-the-bricks\/\">Fix the Bricks<\/a> campaign in Salt Lake City, Utah <\/span><span style=\"font-weight: 400\">has good information on URMs and earthquake safety.\u00a0<\/span>\n\n<i><\/i><strong>Intensity <\/strong><strong>a<\/strong><strong>nd Duration<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">Greater shaking and duration of shaking causes more destruction than lower and shorter shaking.<\/span>\n<p style=\"text-align: left\"><b>[pb_glossary id=\"3103\"]Resonance[\/pb_glossary]<strong>\u2014<\/strong><\/b>[pb_glossary id=\"3103\"]Resonance [\/pb_glossary]occurs when [pb_glossary id=\"3087\"]seismic wave[\/pb_glossary] frequency matches a building\u2019s natural shaking frequency and increases the shaking happened in the 1985 Mexico City Earthquake, where buildings of heights between 6 and 15 stories were especially vulnerable to earthquake damage. Skyscrapers designed with earthquake resilience have dampers and base isolation features to reduce [pb_glossary id=\"3103\"]resonance[\/pb_glossary].<\/p>\n[pb_glossary id=\"3103\"]Resonance[\/pb_glossary] is influenced by the properties of the building materials. Changes in the structural integrity of a building can alter [pb_glossary id=\"3103\"]resonance[\/pb_glossary]<span style=\"font-weight: 400\">. <\/span>Conversely, changes in measured [pb_glossary id=\"3103\"]resonance[\/pb_glossary] can indicate a potentially altered structural integrity.\n\nThese two videos discuss why buildings fall during earthquakes and a modern procedure to reduce potential earthquake destruction for larger buildings.\n\n[caption id=\"attachment_4305\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Why-do-buildings-fall-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-648\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/H4VQul_SmCg[\/embed]\n\n[caption id=\"attachment_4304\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Utah-State-Capital-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-649\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/DP7fB1I7UwE[\/embed]\n<h3><b>9.8.3 Earthquake Recurrence<\/b><\/h3>\n[caption id=\"attachment_3382\" align=\"alignright\" width=\"200\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fault_Trench_RS18376__MG_6182-scaled.jpg\"><img class=\"wp-image-3382 size-medium\" title=\"Taken by: Adam Hiscock, Utah Geological Survey 7\/2\/2014\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fault_Trench_RS18376__MG_6182-scaled-1.jpg\" alt=\"Fault trench near Draper Utah. Trenches allow geologists to see a cross section of a fault and to use dating techniques to determine how frequently earthquakes occur.\" width=\"200\" height=\"300\"><\/a> Fault trench near Draper Utah. Trenches allow geologists to see a cross section of a fault and to use dating techniques to determine how frequently earthquakes occur.[\/caption]\n\n<span style=\"font-weight: 400\">A long hiatus in activity on along a [pb_glossary id=\"3065\"]fault[\/pb_glossary] segment with a history of recurring earthquakes is known as a <strong>[pb_glossary id=\"3087\"]seismic[\/pb_glossary] gap<\/strong>. The lack of activity may indicate the [pb_glossary id=\"3065\"]fault[\/pb_glossary] segment is locked, which may produce a buildup of [pb_glossary id=\"2916\"]strain[\/pb_glossary]\u00a0and higher probability of an earthquake recurring. Geologists dig earthquake trenches across [pb_glossary id=\"3065\"]faults[\/pb_glossary] to estimate the frequency of past earthquake occurrences. Trenches are effective for faults with relatively long <\/span><b>[pb_glossary id=\"3104\"]recurrence[\/pb_glossary] intervals<\/b>, roughly <span style=\"font-weight: 400\">100s to 10,000s of years\u00a0 between significant earthquakes. Trenches are less useful in areas with more frequent earthquakes because they usually have more recorded data. <\/span>\n\n&nbsp;\n<h3><b>9.8.4 Earthquake Distribution<\/b><\/h3>\nThis video shows the distribution of significant earthquakes on the Earth during the years 2010 through 2012. Like [pb_glossary id=\"1181\"]volcanoes[\/pb_glossary], earthquakes tend to aggregate around active boundaries of [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] [pb_glossary id=\"2591\"]plates[\/pb_glossary]. The exception is [pb_glossary id=\"1183\"]intraplate[\/pb_glossary] earthquakes, which are comparatively rare..\n\n[caption id=\"attachment_4306\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/World-Earthquakes-2010-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-651\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/Wc6vtj4yYcY[\/embed]\n\n<strong>[pb_glossary id=\"2602\"]Subduction[\/pb_glossary] Zones<\/strong><strong>\u2014<\/strong><b><i><\/i><\/b><span style=\"font-weight: 400\">[pb_glossary id=\"2602\"]Subduction[\/pb_glossary] zones, found at [pb_glossary id=\"2600\"]convergent[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries, are where the largest and deepest earthquakes, called [pb_glossary id=\"3075\"]megathrust[\/pb_glossary] earthquakes, occur. Examples of [pb_glossary id=\"2602\"]subduction[\/pb_glossary]-zone earthquake areas include the Sumatran Islands, Aleutian Islands, west [pb_glossary id=\"2890\"]coast[\/pb_glossary] of South America, and Cascadia [pb_glossary id=\"2602\"]Subduction[\/pb_glossary] Zone off the coast of Washington and Oregon. <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">\u00a0Chapter 2<\/a><a href=\"http:\/\/opengeology.org\/textbook\/2-plate-tectonics\/#231_Subduction\">\u00a0<\/a> for more information about [pb_glossary id=\"2602\"]subduction[\/pb_glossary] zones.\n\n<strong>[pb_glossary id=\"2620\"]Collision[\/pb_glossary] Zone<\/strong><strong>s<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">Collisions between converging [pb_glossary id=\"2575\"]continental[\/pb_glossary] [pb_glossary id=\"2591\"]plates[\/pb_glossary] create broad earthquake zones that may generate deep, large earthquakes from the remnants of past [pb_glossary id=\"2602\"]subduction[\/pb_glossary] events or other deep-crustal processes. The Himalayan Mountains (northern border of the Indian subcontinent) and Alps (southern Europe and Asia) are active regions of [pb_glossary id=\"2620\"]collision[\/pb_glossary]-zone earthquakes. <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a> for more information about [pb_glossary id=\"2620\"]collision[\/pb_glossary] zones.\n\n<strong>[pb_glossary id=\"2601\"]Transform[\/pb_glossary] <\/strong><strong>Boundaries<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">[pb_glossary id=\"3076\"]Strike-slip[\/pb_glossary] [pb_glossary id=\"3065\"]faults[\/pb_glossary] created at [pb_glossary id=\"2601\"]transform[\/pb_glossary] boundaries produce moderate-to-large earthquakes, usually having a maximum [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] of about 8.\u00a0 The San Andreas [pb_glossary id=\"3065\"]fault[\/pb_glossary] (California) is an example of a [pb_glossary id=\"2601\"]transform[\/pb_glossary]-boundary earthquake zone. Haiti's Enriquillo-Plantain Garden [pb_glossary id=\"3065\"]fault[\/pb_glossary] [pb_glossary id=\"2664\"]system[\/pb_glossary], which caused the 2010 earthquake near Port-au-Prince (see below), and Septentrional [pb_glossary id=\"3065\"]Fault[\/pb_glossary], which destroyed Cap-Ha\u00eftien in 1842 and shook Cuba in 2020, are also [pb_glossary id=\"2601\"]transform[\/pb_glossary] [pb_glossary id=\"3065\"]faults[\/pb_glossary]. Other examples are the Alpine [pb_glossary id=\"3065\"]Fault[\/pb_glossary] (New Zealand) and Anatolian [pb_glossary id=\"3065\"]Faults[\/pb_glossary] (Turkey). <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a> for more information about [pb_glossary id=\"2601\"]transform[\/pb_glossary] boundaries.\n<p style=\"text-align: left\"><strong>[pb_glossary id=\"2599\"]Divergent[\/pb_glossary] Boundaries<\/strong><b>\u2014<\/b><span style=\"font-weight: 400\">[pb_glossary id=\"2575\"]Continental[\/pb_glossary] [pb_glossary id=\"2624\"]rifts[\/pb_glossary] and [pb_glossary id=\"2630\"]mid-ocean ridges[\/pb_glossary] found at [pb_glossary id=\"2599\"]divergent[\/pb_glossary] boundaries generally produce moderate earthquakes. Examples of active earthquake zones include the East African [pb_glossary id=\"2624\"]Rift[\/pb_glossary] [pb_glossary id=\"2664\"]System[\/pb_glossary] (southwestern Asia through eastern Africa), Iceland, and [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] province (Nevada, Utah, California, Arizona, and northwestern Mexico). <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a> for more information about [pb_glossary id=\"2599\"]divergent[\/pb_glossary] boundaries.<\/p>\n\n[caption id=\"attachment_3383\" align=\"alignright\" width=\"354\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_.png\"><img class=\"wp-image-652\" title=\"By Kbh3rd (Own work) [CC BY-SA 3.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_.png\" alt=\"Map showing concentration of earthquakes near the border of Missouri, Kentucky, Tennessee, and Illinois\" width=\"354\" height=\"373\"><\/a> High density of earthquakes in the New Madrid seismic zone.[\/caption]\n<p style=\"text-align: left\"><strong>[pb_glossary id=\"1183\"]Intraplate[\/pb_glossary] Earthquakes<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">[pb_glossary id=\"1183\"]Intraplate[\/pb_glossary] earthquakes are not found near [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries, but generally occur in areas of weakened [pb_glossary id=\"2580\"]crust[\/pb_glossary] or [pb_glossary id=\"3333\"]concentrated[\/pb_glossary] [pb_glossary id=\"2918\"]tectonic stress[\/pb_glossary]. The New Madrid [pb_glossary id=\"3087\"]seismic[\/pb_glossary] zone, which covers Missouri, Illinois, Tennessee, Arkansas, and Indiana, is thought to represent the failed Reelfoot [pb_glossary id=\"2624\"]rift[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. <\/span>The failed [pb_glossary id=\"2624\"]rift[\/pb_glossary] zone weakened the [pb_glossary id=\"2580\"]crust[\/pb_glossary], making it more responsive to [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] movement and interaction. Geologists theorize the infrequently occurring earthquakes are produced by low [pb_glossary id=\"2916\"]strain[\/pb_glossary] rates<\/p>\n\n<h3><b>9.8.5 Secondary Hazards Caused by Earthquakes<\/b><\/h3>\n<p style=\"text-align: left\">Most earthquake damage is caused by ground shaking and fault block displacement\u00a0 In addition, there are secondary hazards that endanger structures and people, in some cases after the shaking stops.<\/p>\n\n\n[caption id=\"attachment_2478\" align=\"alignright\" width=\"500\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Liquefaction_at_Niigata-1.jpg\"><img class=\"wp-image-44 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction_at_Niigata-1.jpg\" alt=\"Buildings toppled from liquefaction during a 7.5 magnitude earthquake in Japan.\" width=\"500\" height=\"297\"><\/a> Buildings toppled from liquefaction during a 7.5 magnitude earthquake in Japan.[\/caption]\n\nBuildings toppled from liquefaction during a 7.5 magnitude earthquake in Japan.\n<p style=\"text-align: left\"><span style=\"font-weight: 400\"><strong>[pb_glossary id=\"3106\"]Liquefaction[\/pb_glossary]\u2014<\/strong>[pb_glossary id=\"3106\"]Liquefaction[\/pb_glossary] occurs when water-[pb_glossary id=\"2706\"]saturated[\/pb_glossary], unconsolidated [pb_glossary id=\"2678\"]sediments[\/pb_glossary], usually silt or sand, become fluid-like from shaking. The shaking breaks the [pb_glossary id=\"2692\"]cohesion[\/pb_glossary] between grains of [pb_glossary id=\"2678\"]sediment[\/pb_glossary], creating a slurry of particles suspended in water. Buildings settle or tilt in the liquified [pb_glossary id=\"2678\"]sediment[\/pb_glossary], which looks very much like quicksand in the movies. [pb_glossary id=\"3106\"]Liquefaction[\/pb_glossary] also creates sand [pb_glossary id=\"1181\"]volcanoes[\/pb_glossary], cone-shaped features created when liquefied sand is squirted through an overlying and usually finer-grained layer.<\/span><\/p>\nThis video demonstrates how [pb_glossary id=\"3106\"]liquefaction[\/pb_glossary] takes place.\n\n[caption id=\"attachment_4299\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Liquefaction-Demonstrated-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-653\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/b_aIm5oi5eA[\/embed]\n\nThis video shows [pb_glossary id=\"3106\"]liquefaction[\/pb_glossary] occurring during the 2011 earthquake in Japan.\n\n[caption id=\"attachment_4298\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-654\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/rn3oAvmZY8k[\/embed]\n\n<strong>[pb_glossary id=\"3194\"]Tsunamis[\/pb_glossary]<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">Among the most devastating natural disasters are [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary], earthquake-induced ocean waves. When the sea floor is [pb_glossary id=\"3081\"]offset[\/pb_glossary] by [pb_glossary id=\"3065\"]fault[\/pb_glossary] movement or an underwater [pb_glossary id=\"1199\"]landslide[\/pb_glossary], the ground displacement lifts a volume of ocean water and generates the [pb_glossary id=\"3194\"]tsunami[\/pb_glossary] wave. Ocean wave behavior, which includes [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary], is covered in <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/12-shorelines\/\">Chapter 12<\/a>. [pb_glossary id=\"3194\"]Tsunami[\/pb_glossary] waves are fast-moving with low [pb_glossary id=\"3184\"]amplitude[\/pb_glossary] in deep ocean water but grow significantly in [pb_glossary id=\"3184\"]amplitude[\/pb_glossary] in the shallower waters approaching [pb_glossary id=\"3195\"]shore[\/pb_glossary]. <\/span>When a [pb_glossary id=\"3194\"]tsunami[\/pb_glossary] is about to [pb_glossary id=\"1453\"]strike[\/pb_glossary] land, the drawback of the [pb_glossary id=\"3183\"]trough[\/pb_glossary] preceding the [pb_glossary id=\"3182\"]wave crest[\/pb_glossary] causes the water to recede dramatically from [pb_glossary id=\"3195\"]shore[\/pb_glossary]. Tragically, curious people wander out and follow the disappearing water, only to be overcome by an oncoming wall of water that can be upwards of a 30 m (100 ft) high. Early warning systems help mitigate the loss of life caused by [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary].\n\n[caption id=\"attachment_3385\" align=\"alignleft\" width=\"429\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.8_Propagation_tsunami.gif\"><img class=\"wp-image-655 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.8_Propagation_tsunami.gif\" alt=\"Animated gif showing large wavelength, low-amplitude waves in the deep ocean and high-amplitude, low-wavelength waves in the shallow ocean. Frequency decreases with depth.\" width=\"429\" height=\"225\"><\/a> As the ocean depth becomes shallower, the wave slows down and pile up on top of itself, making large, high-amplitude waves.[\/caption]\n\n&nbsp;\n\n[caption id=\"attachment_3387\" align=\"alignright\" width=\"431\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/RS13929_S2120-scr.jpg\"><img class=\"wp-image-656\" title=\"https:\/\/geodata.geology.utah.gov\/pages\/view.php?ref=13929&amp;amp;k=&amp;amp;search=springdale&amp;amp;offset=144&amp;amp;order_by=date&amp;amp;sort=DESC&amp;amp;archive=0\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-300x212.jpg\" alt=\"Broken house offset and destroyed from a landslide.\" width=\"431\" height=\"305\"><\/a> House in Springdale, Utah destroyed by earthquake-triggered landslide.[\/caption]\n\n<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"1199\"]Landslides[\/pb_glossary]\u2014<\/strong><\/span>Shaking can [pb_glossary id=\"3117\"]trigger[\/pb_glossary] [pb_glossary id=\"1199\"]landslides[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/10-mass-wasting\/\">Chapter 10<\/a>). In 1992 a [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 5.9 earthquake in St. George, Utah, caused a [pb_glossary id=\"1199\"]landslide[\/pb_glossary] that destroyed several structures in the Balanced Rock Hills subdivision in Springville, Utah<span style=\"font-weight: 400\">.\u00a0\u00a0<\/span>\n\n<strong>Seiches<\/strong><strong>\u2014S<\/strong>eiches are waves generated in lakes by earthquakes. The shaking may cause water to slosh back-and-forth or sometimes change the lake depth. Seiches in Hebgen Lake during a 1959 earthquake caused major destruction to nearby structures and roads.\n\nThis video shows a seich generated in a swimming pool by an earthquake in Nepal in 2015.\n\n[caption id=\"attachment_4296\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Earthquake-Nepal-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-657\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/youtu.be\/27GMnYEWL0M[\/embed]\n\n&nbsp;\n<h4><\/h4>\n<strong>Land Elevation Changes<\/strong><strong>\u2014<\/strong>[pb_glossary id=\"3079\"]Elastic rebound[\/pb_glossary] and displacement along the [pb_glossary id=\"3065\"]fault[\/pb_glossary] plane can cause significant land elevation changes, such as [pb_glossary id=\"1464\"]subsidence[\/pb_glossary] or upheaval. The 1964 Alaska earthquake produced significant land elevation changes, with the differences in height between the [pb_glossary id=\"3067\"]hanging wall[\/pb_glossary] and [pb_glossary id=\"3068\"]footwall[\/pb_glossary] ranging from one to several meters (3\u201330 ft). The Wasatch Mountains in Utah represent an accumulation of [pb_glossary id=\"3107\"]fault scarps[\/pb_glossary] created a few meters at a time, over a few million years.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"64\"]\n\n[caption id=\"attachment_4315\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.8-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-658\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.8 via this QR Code.[\/caption]\n<h2><strong>9.9 Case Studies<\/strong><\/h2>\nVideo explaining the [pb_glossary id=\"3087\"]seismic[\/pb_glossary] activity and hazards of the Intermountain [pb_glossary id=\"3087\"]Seismic[\/pb_glossary] Belt and the Wasatch [pb_glossary id=\"3065\"]Fault[\/pb_glossary], a large [pb_glossary id=\"1183\"]intraplate[\/pb_glossary] area of [pb_glossary id=\"3087\"]seismic[\/pb_glossary] activity.\n\n[caption id=\"attachment_4323\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Wasatch-Fault-Fly-By-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-659\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/DByPiCkznE0[\/embed]\n<h3><b>9.9.1 North American Earthquakes<\/b><\/h3>\n<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] Earthquakes\u2014<\/strong>Earthquakes in the [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] Province, <\/span>from the Wasatch [pb_glossary id=\"3065\"]Fault[\/pb_glossary] (Utah) to the Sierra Nevada (California), occur primarily in normal [pb_glossary id=\"3065\"]faults[\/pb_glossary] created by [pb_glossary id=\"1445\"]tensional[\/pb_glossary] forces. The Wasatch [pb_glossary id=\"3065\"]Fault[\/pb_glossary], which defines the eastern extent of the [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] province, has been studied as an earthquake hazard for more than 100 years.\n\n<b>New Madrid Earthquakes (1811-1812)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b><span style=\"font-weight: 400\">Historical accounts of earthquakes in the New Madrid [pb_glossary id=\"3087\"]seismic[\/pb_glossary] zone date as far back as 1699 and earthquakes continue to be reported in modern times<\/span><span style=\"font-weight: 400\">. A sequence of large (M<sub>w<\/sub> &gt;7) occurred from December 1811 to February 1812 in the New Madrid area of Missouri<\/span><span style=\"font-weight: 400\">. The earthquakes damaged houses in St. Louis, affected the [pb_glossary id=\"3134\"]stream[\/pb_glossary] course of the Mississippi [pb_glossary id=\"3134\"]River[\/pb_glossary], and leveled the town of New Madrid. \u00a0These earthquakes were the result of [pb_glossary id=\"1183\"]intraplate[\/pb_glossary] [pb_glossary id=\"3087\"]seismic[\/pb_glossary] activity<\/span><span style=\"font-weight: 400\">.\u00a0<\/span>\n\n<b>Charleston (1886)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b><span style=\"font-weight: 400\">The 1886 earthquake in Charleston South Carolina was a [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 7.0, with a [pb_glossary id=\"3101\"]Mercalli[\/pb_glossary] intensity of X, caused significant ground motion, and killed at least 60 people. \u00a0This [pb_glossary id=\"1183\"]intraplate[\/pb_glossary] earthquake was likely associated with ancient [pb_glossary id=\"3065\"]faults[\/pb_glossary] created during the breakup of [pb_glossary id=\"3366\"]Pangea[\/pb_glossary]. \u00a0The earthquake caused significant [pb_glossary id=\"3106\"]liquefaction[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. Scientists estimate the [pb_glossary id=\"3104\"]recurrence[\/pb_glossary] of destructive earthquakes in this area with an interval of approximately 1500 to 1800 years.<\/span>\n\n<b>Great San Francisco Earthquake and Fire (1906)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><span style=\"font-weight: 400\">On April 18, 1906, a large earthquake, with an estimated [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] of 7.8 and MMI of X, occurred along the San Andreas [pb_glossary id=\"3065\"]fault[\/pb_glossary] near San Francisco California. There were multiple [pb_glossary id=\"3084\"]aftershocks[\/pb_glossary] followed by devastating fires, resulting in about 80% of the city being destroyed. Geologists G.K. Gilbert and Richard L. Humphrey, working <\/span><\/b>independently, arrived the day following the earthquake and took measurements and photographs<b><span style=\"font-weight: 400\">.\u00a0<\/span><\/b>\n\n[caption id=\"attachment_3388\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/1200px-San_Francisco_1906_earthquake_Panoramic_View.jpg\"><img class=\"size-large wp-image-660\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-1024x129.jpg\" alt=\"Wide view of rubble and skeletons of buildings that remain, some still smoking.\" width=\"1024\" height=\"129\"><\/a> Remains of San Francisco after the 1906 earthquake and fire.[\/caption]\n<p style=\"text-align: left\"><b>Alaska (1964)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b>The 1964 Alaska earthquake, [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 9.2, was one of the most powerful earthquakes ever recorded. The earthquake originated in a [pb_glossary id=\"3075\"]megathrust[\/pb_glossary] [pb_glossary id=\"3065\"]fault[\/pb_glossary] along the Aleutian [pb_glossary id=\"2602\"]subduction[\/pb_glossary] zone. The earthquake caused large areas of land [pb_glossary id=\"1464\"]subsidence[\/pb_glossary] and uplift, as well as significant [pb_glossary id=\"3110\"]mass wasting[\/pb_glossary].<\/p>\nVideo from the USGS about the 1964 Alaska earthquake.\n\n[caption id=\"attachment_4291\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/1964-Quake-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-661\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/lE2j10xyOgI[\/embed]\n\n<b>Loma Prieta (1989)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b>The Loma Prieta, California, earthquake was created by movement along the San Andreas [pb_glossary id=\"3065\"]Fault[\/pb_glossary]. The [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 6.9 earthquake was followed by a [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] 5.2 [pb_glossary id=\"3084\"]aftershock[\/pb_glossary]. It caused 63 deaths, buckled portions of the several freeways, and collapsed part of the San Francisco-Oakland Bay Bridge.\n\nThis video shows how shaking propagated across the Bay Area during the 1989 Loma Prieta earthquake.\n\n[caption id=\"attachment_4317\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.9-Video-QR-Code.png\"><img class=\"size-thumbnail wp-image-662\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this interactive activity via this QR Code.[\/caption]\n\n[video width=\"300\" height=\"200\" webm=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Lp1989plan_hires.webm\"][\/video]\n\n<span style=\"font-weight: 400\">This video shows destruction caused by the 1989 Loma Prieta earthquake.<\/span>\n\n[caption id=\"attachment_4300\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Loma-Prieta-Earthquake-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-663\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/L6jYgqLyIPw[\/embed]\n<h3><b>9.9.2 Global Earthquakes<\/b><\/h3>\nMany of history\u2019s largest earthquakes occurred in [pb_glossary id=\"3075\"]megathrust[\/pb_glossary] zones, such as the Cascadia [pb_glossary id=\"2602\"]Subduction[\/pb_glossary] Zone (Washington and Oregon coasts) and Mt. Rainier (Washington).\n\n<b>Shaanxi, China (1556)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b><span style=\"font-weight: 400\">On January 23, 1556 an earthquake of an approximate [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 8 hit central China, killing approximately 830,000 people in what is considered the most deadly earthquake in history.\u00a0<\/span><b><span style=\"font-weight: 400\">The high death toll was attributed to the collapse of cave dwellings (<span style=\"font-style: normal !msorm\"><em>yaodong<\/em><\/span>) built in [pb_glossary id=\"2909\"]loess[\/pb_glossary] deposits, which are large banks of windblown, compacted [pb_glossary id=\"2678\"]sediment[\/pb_glossary] (see<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">\u00a0Chapter 5<\/a>). <\/span><\/b>Earthquakes in this are region are believed to have a [pb_glossary id=\"3104\"]recurrence[\/pb_glossary] interval of 1000 years.\n\n<strong>Lisbon, Portugal (1755)<b><span style=\"font-weight: 400\">\u2014On November 1, 1755 an earthquake with an estimated [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] range of 8\u20139 struck Lisbon, Portugal<\/span><\/b><\/strong><span style=\"font-weight: 400\">, killing between 10,000 to 17,400 people<\/span><span style=\"font-weight: 400\">. The earthquake was followed by a [pb_glossary id=\"3194\"]tsunami[\/pb_glossary], which brought the total death toll to between 30,000-70,000 people.<\/span>\n\n<strong>Valdivia, Chile (1960)<b><span style=\"font-weight: 400\">\u2014The May 22, 1960 earthquake was the most powerful earthquake ever measured, with a [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 9.4\u20139.6 and lasting an estimated 10 minutes. <\/span><\/b><\/strong>It triggered [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary] that destroyed houses across the Pacific Ocean in Japan and Hawaii and caused vents to erupt on the Puyehue-Cord\u00f3n Caulle (Chile).\n\nVideo describing the [pb_glossary id=\"3194\"]tsunami[\/pb_glossary] produced by the 1960 Chili earthquake.\n\n[caption id=\"attachment_4318\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Tsunami-Animation-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-664\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/RHYbprZAIWo[\/embed]\n\n<b>Tangshan, China (1976)<strong><span style=\"font-weight: 400\">\u2014<\/span><\/strong><\/b>Just before 4 a.m. (Beijing time) on July 28, 1976 a [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 7.8 earthquake struck Tangshan (Hebei Province), China, and killed more than 240,000 people. The high death-toll is attributed to people still being asleep or at home and most buildings being made of unreinforced masonry.\n\n<strong>Sumatra, Indonesia (2004)<b><span style=\"font-weight: 400\">\u2014On December 26, 2004, slippage of the Sunda [pb_glossary id=\"3075\"]megathrust[\/pb_glossary] [pb_glossary id=\"3065\"]fault[\/pb_glossary] generated a [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 9.0\u20139.3 earthquake off the [pb_glossary id=\"2890\"]coast[\/pb_glossary] of Sumatra, Indonesia<\/span><\/b><\/strong><span style=\"font-weight: 400\">. This [pb_glossary id=\"3075\"]megathrust[\/pb_glossary] fault is created by the Australia [pb_glossary id=\"2591\"]plate[\/pb_glossary] [pb_glossary id=\"2602\"]subducting[\/pb_glossary] below the Sunda plate in the Indian Ocean. <\/span>The resultant [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary] created [pb_glossary id=\"1933\"]massive[\/pb_glossary] waves as tall as 24 m (79 ft) when they reached the [pb_glossary id=\"3195\"]shore[\/pb_glossary] and killed more than an estimated 200,000 people along the Indian Ocean [pb_glossary id=\"2890\"]coastline[\/pb_glossary].\n\n<b>Haiti (2010)<strong><span style=\"font-weight: 400\">\u2014<\/span><\/strong><\/b>The [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 7 earthquake that occurred on January 12, 2010, was followed by many [pb_glossary id=\"3084\"]aftershocks[\/pb_glossary] of [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] 4.5 or higher. More than 200,000 people are estimated to have died as result of the earthquake. The widespread infrastructure damage and crowded conditions contributed to a cholera outbreak, which is estimated to have caused thousands more deaths.\n\n<strong>T\u014dhoku, Japan (2011)<b><span style=\"font-weight: 400\">\u2014<\/span><\/b><\/strong>Because most Japanese buildings are designed to tolerate earthquakes, the [pb_glossary id=\"3100\"]moment magnitude[\/pb_glossary] 9.0 earthquake on March 11, 2011, was not as destructive as the [pb_glossary id=\"3194\"]tsunami[\/pb_glossary] it created. The [pb_glossary id=\"3194\"]tsunami[\/pb_glossary] caused more than 15,000 deaths and tens of billions of dollars in damage, including the destructive meltdown of the Fukushima nuclear power plant.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"65\"]\n\n[caption id=\"attachment_4316\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.9-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-665\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 9.9 via this QR Code.[\/caption]\n<h2>Summary<\/h2>\nGeologic [pb_glossary id=\"2915\"]stress[\/pb_glossary], applied force, comes in three types: [pb_glossary id=\"1445\"]tension[\/pb_glossary], [pb_glossary id=\"1447\"]shear[\/pb_glossary], and [pb_glossary id=\"1446\"]compression[\/pb_glossary]. [pb_glossary id=\"2916\"]Strain[\/pb_glossary] is produced by [pb_glossary id=\"2915\"]stress[\/pb_glossary] and produces three types of [pb_glossary id=\"1448\"]deformation[\/pb_glossary]: elastic, [pb_glossary id=\"2582\"]ductile[\/pb_glossary], and [pb_glossary id=\"2583\"]brittle[\/pb_glossary]. Geological maps are two-dimensional representations of surface [pb_glossary id=\"2960\"]formations[\/pb_glossary] which are the surface expression of three-dimensional geologic structures in the subsurface. The map symbol called [pb_glossary id=\"1453\"]strike[\/pb_glossary] and [pb_glossary id=\"1454\"]dip[\/pb_glossary] or rock attitude indicates the orientation of rock [pb_glossary id=\"2857\"]strata[\/pb_glossary] with reference to north-south and horizontal. Folded rock layers are categorized by the orientation of their limbs, [pb_glossary id=\"1455\"]fold[\/pb_glossary] axes and [pb_glossary id=\"1456\"]axial planes[\/pb_glossary]. [pb_glossary id=\"3065\"]Faults[\/pb_glossary] result when [pb_glossary id=\"2915\"]stress[\/pb_glossary] forces exceed rock integrity and friction, leading to [pb_glossary id=\"1452\"]brittle deformation[\/pb_glossary] and breakage. The three major [pb_glossary id=\"3065\"]fault[\/pb_glossary] types are described by the movement of their fault blocks: normal, [pb_glossary id=\"3076\"]strike-slip[\/pb_glossary], and reverse.\n\nEarthquakes, or [pb_glossary id=\"3087\"]seismic[\/pb_glossary] activity, are caused by sudden [pb_glossary id=\"1452\"]brittle deformation[\/pb_glossary] accompanied by [pb_glossary id=\"3079\"]elastic rebound[\/pb_glossary]. The release of energy from an earthquake [pb_glossary id=\"3080\"]focus[\/pb_glossary] is generated as [pb_glossary id=\"3087\"]seismic[\/pb_glossary] waves. P and [pb_glossary id=\"3090\"]S waves[\/pb_glossary] travel through the Earth\u2019s interior. When they [pb_glossary id=\"1453\"]strike[\/pb_glossary] the outer [pb_glossary id=\"2580\"]crust[\/pb_glossary], they create [pb_glossary id=\"3089\"]surface waves[\/pb_glossary]. Human activities, such as mining and nuclear detonations, can also cause [pb_glossary id=\"3087\"]seismic[\/pb_glossary] activity. [pb_glossary id=\"3095\"]Seismographs[\/pb_glossary] measure the energy released by an earthquake using a logarithmic scale of [pb_glossary id=\"3098\"]magnitude[\/pb_glossary] units; the [pb_glossary id=\"3100\"]Moment Magnitude[\/pb_glossary] Scale has replaced the original [pb_glossary id=\"3099\"]Richter Scale[\/pb_glossary]. Earthquake intensity is the perceived effects of ground shaking and physical damage. The location of earthquake foci is determined from triangulation readings from multiple [pb_glossary id=\"3095\"]seismographs[\/pb_glossary].\n\nEarthquake rays passing through rocks of the Earth\u2019s interior and measured at the [pb_glossary id=\"3095\"]seismographs[\/pb_glossary] of the worldwide [pb_glossary id=\"3087\"]Seismic[\/pb_glossary] Network allow 3-D imaging of buried rock masses as [pb_glossary id=\"3087\"]seismic[\/pb_glossary] tomographs.\n\nEarthquakes are associated with [pb_glossary id=\"2576\"]plate tectonics[\/pb_glossary]. They usually occur around the active [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries, including zones of [pb_glossary id=\"2602\"]subduction[\/pb_glossary], [pb_glossary id=\"2620\"]collision[\/pb_glossary], and [pb_glossary id=\"2601\"]transform[\/pb_glossary] and [pb_glossary id=\"2599\"]divergent[\/pb_glossary] boundaries. Areas of [pb_glossary id=\"1183\"]intraplate[\/pb_glossary] earthquakes also occur. The damage caused by earthquakes depends on a number of factors, including [pb_glossary id=\"3098\"]magnitude[\/pb_glossary], location and direction, local conditions, building materials, intensity and duration, and [pb_glossary id=\"3103\"]resonance[\/pb_glossary]. In addition to damage directly caused by ground shaking, secondary earthquake hazards include [pb_glossary id=\"3106\"]liquefaction[\/pb_glossary], [pb_glossary id=\"3194\"]tsunamis[\/pb_glossary], [pb_glossary id=\"1199\"]landslides[\/pb_glossary], seiches, and elevation changes.\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n[h5p id=\"66\"]\n\n[caption id=\"attachment_4294\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Ch.9-Review-QR-Code.png\"><img class=\"size-thumbnail wp-image-666\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the review quiz for Chapter 9 via this QR Code.[\/caption]\n<h2>References<\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n \t<li class=\"csl-entry\">Christenson, G.E., 1995, The September 2, 1992 ML 5.8 St. George earthquake, Washington County, Utah: Utah Geological Survey Circular 88, 48 p.<\/li>\n \t<li class=\"csl-entry\">Coleman, J.L., and Cahan, S.M., 2012, Preliminary catalog of the [pb_glossary id=\"1463\"]sedimentary basins[\/pb_glossary] of the United States: U.S. Geological Survey Open-File Report 1111, 27 p.<\/li>\n \t<li class=\"csl-entry\">Earle, S., 2015, Physical geology OER textbook: BC Campus OpenEd.<\/li>\n \t<li class=\"csl-entry\">Feldman, J., 2012, When the Mississippi Ran Backwards: Empire, Intrigue, Murder, and the New Madrid Earthquakes of 1811 and 1812: Free Press, 320 p.<\/li>\n \t<li class=\"csl-entry\">Fuller, M.L., 1912, The New Madrid earthquake: Central United States Earthquake Consortium Bulletin 494, 129 p.<\/li>\n \t<li class=\"csl-entry\">Gilbert, G.K., and Dutton, C.E., 1877, Report on the geology of the Henry Mountains: Washington, U.S. Government Printing Office, 160 p.<\/li>\n \t<li class=\"csl-entry\">Hildenbrand, T.G., and Hendricks, J.D., 1995, Geophysical setting of the Reelfoot [pb_glossary id=\"2624\"]rift[\/pb_glossary] and relations between [pb_glossary id=\"2624\"]rift[\/pb_glossary] structures and the New Madrid [pb_glossary id=\"3087\"]seismic[\/pb_glossary] zone: U.S. Geological Survey Professional Paper 1538-E, 36 p.<\/li>\n \t<li class=\"csl-entry\">Means, W.D., 1976, [pb_glossary id=\"2915\"]Stress[\/pb_glossary] and [pb_glossary id=\"2916\"]Strain[\/pb_glossary] - Basic Concepts of Continuum Mechanics: Berlin, Springe, 273 p.<\/li>\n \t<li class=\"csl-entry\">Ressetar, R. (Ed.), 2013, The San Rafael Swell and Henry Mountains [pb_glossary id=\"1461\"]Basin[\/pb_glossary]: geologic centerpiece of Utah: Utah Geological Association, Utah Geological Association, 250 p.<\/li>\n \t<li class=\"csl-entry\">Satake, K., and Atwater, B.F., 2007, Long-Term Perspectives on Giant Earthquakes and [pb_glossary id=\"3194\"]Tsunamis[\/pb_glossary] at [pb_glossary id=\"2602\"]Subduction[\/pb_glossary] Zones: Annual Review of Earth and Planetary Sciences, v. 35, no. 1, p. 349\u2013374., doi: <a href=\"https:\/\/doi.org\/10.1146\/annurev.earth.35.031306.140302\">10.1146\/annurev.earth.35.031306.140302<\/a>.<\/li>\n \t<li class=\"csl-entry\">Talwani, P., and Cox, J., 1985, Paleoseismic evidence for [pb_glossary id=\"3104\"]recurrence[\/pb_glossary] of Earthquakes near Charleston, South Carolina: Science, v. 229, no. 4711, p. 379\u2013381.<\/li>\n<\/ol>\n<\/div>","rendered":"<figure id=\"attachment_3347\" aria-describedby=\"caption-attachment-3347\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-e1494992495928-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3347 size-large\" title=\"James St. John https:\/\/commons.wikimedia.org\/wiki\/File:Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01.jpg Pennsylvanian Honaker Trail Formation\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-e1494992495928-scaled-1.jpg\" alt=\"Roadcut outcrop of multicolor rock beds offset by a normal fault.\" width=\"1024\" height=\"527\" \/><\/a><figcaption id=\"caption-attachment-3347\" class=\"wp-caption-text\">Example of a normal fault in an outcrop of the Pennsylvanian Honaker Trail Formation near Moab, Utah.<\/figcaption><\/figure>\n<p><b>KEY CONCEPTS<\/b><\/p>\n<p><b>By the end of this chapter, students should be able to:<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\">\n<ul>\n<li>Differentiate between <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a><\/li>\n<li>Identify the three major types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a><\/li>\n<li>Differentiate between <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2583\">brittle<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2582\">ductile<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1449\">elastic deformation<\/a><\/li>\n<li>Describe the geological map symbol used for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a><\/li>\n<\/ul>\n<ul>\n<li>Name and describe different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> types<\/li>\n<li>Differentiate the three major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> types and describe their associated movements<\/li>\n<li>Explain how <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3079\">elastic rebound<\/a> relates to earthquakes<\/li>\n<\/ul>\n<ul>\n<li>Describe different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic wave<\/a> types and how they are measured<\/li>\n<li>Explain how humans can induce seismicity<\/li>\n<li>Describe how <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> work to record earthquake waves<\/li>\n<li>From <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismograph<\/a> records, locate the epicenter of an earthquake<\/li>\n<li>Explain the difference between earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> and intensity<\/li>\n<li>List earthquake factors that determine ground shaking and destruction<\/li>\n<li>Identify secondary earthquake hazards<\/li>\n<li>Describe notable historical earthquakes<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>Crustal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1448\">deformation<\/a> occurs when applied forces exceed the internal strength of rocks, physically changing their shapes. These forces are called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a>, and the physical changes they create are called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a>.\u00a0Forces involved in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3383\">tectonic<\/a> processes as well as gravity and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2675\">igneous<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1965\">pluton<\/a> emplacement produce <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strains<\/a> in rocks that include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1934\">fractures<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a>.\u00a0When rock experiences large amounts of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1447\">shear<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> and breaks with rapid, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">brittle deformation<\/a>, energy is released in the form of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves, commonly known as an earthquake.<\/p>\n<h2><strong>9.1 Stress and Strain<\/strong><\/h2>\n<figure id=\"attachment_3348\" aria-describedby=\"caption-attachment-3348\" style=\"width: 341px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/stress_types.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-603 size-full\" title=\"Source: USGS https:\/\/earthquake.usgs.gov\/learn\/glossary\/images\/stress_types.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/stress_types.gif\" alt=\"Tensional stress where dominant stresses are pulling away from the object, compressional stress where dominant stress is pushing in towards the object, and shear, where part of the object is pushed and part of the object is pulled (stresses in opposite directions)\" width=\"341\" height=\"271\" \/><\/a><figcaption id=\"caption-attachment-3348\" class=\"wp-caption-text\">Types of stress. Clockwise from top left: tensional stress, compressional stress, and shear stress, and some examples of resulting strain.<\/figcaption><\/figure>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">Stress<\/a><\/b><span style=\"font-weight: 400\"> is the force exerted per unit area and <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a><\/b><span style=\"font-weight: 400\"> is the physical change that results in response to that force. When applied <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> is greater than the internal strength of rock, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> results in the form of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1448\">deformation<\/a> of the rock caused by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a>. \u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">Strain<\/a> in rocks can be represented as a change in rock volume and\/or rock shape, as well as fracturing the rock. \u00a0There are three types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a>: <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">tensional<\/a><\/b>, <b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compressional<\/a><\/b>, and <b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1447\">shear<\/a><\/b><span style=\"font-weight: 400\">. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">Tensional<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> involves forces pulling in opposite directions, which results in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> that stretches and thins rock. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">Compressional<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> involves forces pushing together, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compressional<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> shows up as rock folding and thickening. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1447\">Shear<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> involves transverse forces; the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> shows up as opposing blocks or regions of material moving past each other.<\/span><\/p>\n<p>Table showing types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> and resulting <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a>:<\/p>\n<table style=\"width: 100%\">\n<tbody>\n<tr>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 19.7349%\"><b>Type of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">Stress<\/a><\/b><\/td>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 35.3461%\"><b>Associated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2592\">Plate Boundary<\/a> type (see Ch. 2)<\/b><\/td>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 21.0604%\"><b>Resulting <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">Strain<\/a><\/b><\/td>\n<td style=\"background-color: #79f7b2;text-align: center;vertical-align: middle;width: 23.7113%\"><b>Associated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3081\">offset<\/a> types<\/b><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;vertical-align: middle;width: 19.7349%\"><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">Tensional<\/a><\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 35.3461%\"><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2599\">divergent<\/a><\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 21.0604%\"><span style=\"font-weight: 400\">Stretching and thinning<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 23.7113%\"><span style=\"font-weight: 400\">Normal<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;vertical-align: middle;width: 19.7349%\"><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">Compressional<\/a><\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 35.3461%\"><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2600\">convergent<\/a><\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 21.0604%\"><span style=\"font-weight: 400\">Shortening and thickening<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 23.7113%\"><span style=\"font-weight: 400\">Reverse<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;vertical-align: middle;width: 19.7349%\"><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1447\">Shear<\/a><\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 35.3461%\"><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a><\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 21.0604%\"><span style=\"font-weight: 400\">Tearing<\/span><\/td>\n<td style=\"text-align: center;vertical-align: middle;width: 23.7113%\"><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">Strike-slip<\/a><\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-57\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-57\" class=\"h5p-iframe\" data-content-id=\"57\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.1 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4307\" aria-describedby=\"caption-attachment-4307\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.1-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-604\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.1-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4307\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.1 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>9.2 Deformation<\/strong><\/h2>\n<figure id=\"attachment_3349\" aria-describedby=\"caption-attachment-3349\" style=\"width: 413px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/response-of-geological-materials-to-stress.png\" rel=\"https:\/\/opentextbc.ca\/geology\/wp-content\/uploads\/sites\/110\/2015\/08\/response-of-geological-materials-to-stress.png noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-605\" title=\"Physical Geology by Steven Earle at https:\/\/opentextbc.ca\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-300x214.png\" alt=\"Chart demonstrating the deformation of different materials when stress is applied.\" width=\"413\" height=\"295\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-300x214.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-1024x732.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-768x549.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-65x46.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-225x161.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress-350x250.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/response-of-geological-materials-to-stress.png 1368w\" sizes=\"auto, (max-width: 413px) 100vw, 413px\" \/><\/a><figcaption id=\"caption-attachment-3349\" class=\"wp-caption-text\">Different materials deform differently when stress is applied. Material &#8220;A&#8221; has relatively little deformation when undergoing large amounts of stress, before undergoing plastic deformation, and finally brittlely failing. Material &#8220;B&#8221; only elastically deforms before brittlely failing. Material &#8220;C&#8221; undergoes significant plastic deformation before finally failing brittlely.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">When rocks are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stressed<\/a>, the resulting <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> can be elastic, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2582\">ductile<\/a>, or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2583\">brittle<\/a>. This change is generally called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1448\">deformation<\/a><\/strong>.\u00a0<\/span><b>Elastic\u00a0<\/b><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1448\">deformation<\/a><\/b><span style=\"font-weight: 400\"> is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> that is reversible after a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> is released. \u00a0For example, when you stretch a rubber <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2931\">band<\/a>, it elastically returns to its original shape after you release it. <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1450\">Ductile deformation<\/a><\/b><span style=\"font-weight: 400\"> occurs when enough <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> is applied to a material that the changes in its shape are permanent, and the material is no longer able to revert to its original shape. For example, if you bend a metal bar too far, it can be permanently bent out of shape. <\/span>The point at which <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1449\">elastic deformation<\/a> is surpassed and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> becomes permanent is called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1451\">yield point<\/a><\/strong>. In the figure, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1451\">yield point<\/a> is where the line transitions from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1449\">elastic deformation<\/a> to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1450\">ductile deformation<\/a> (the end of the dashed line). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">Brittle deformation<\/a> is another critical point of no return, when rock integrity fails and the rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1934\">fractures<\/a> under increasing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a>.<\/p>\n<p><span style=\"font-weight: 400\">The type of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1448\">deformation<\/a> a rock undergoes depends on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3116\">pore<\/a> pressure, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> rate, rock strength, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2689\">temperature<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> intensity, time, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2917\">confining<\/a> pressure. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3116\">Pore<\/a> pressure is exerted on the rock by fluids in the open spaces or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3116\">pores<\/a> embedded within rock or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediment<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">Strain<\/a> rate measures how quickly a material is deformed. For example, applying <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> slowly makes it is easier to bend a piece of wood without breaking it. Rock strength measures how easily a rock deforms under <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2839\">Shale<\/a> has low strength and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1962\">granite<\/a> has high strength. Removing heat, or decreasing the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2689\">temperature<\/a>, makes materials more rigid and susceptible to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">brittle deformation<\/a>. On the other hand, heating materials make them more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2582\">ductile<\/a> and less <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2583\">brittle<\/a>. Heated glass can be bent and stretched.<\/span><\/p>\n<p><span style=\"font-weight: 400\">Table showing relationship between factors operating on rock and the resulting <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strains<\/a>:<\/span><\/p>\n<table style=\"width: 786px\">\n<tbody>\n<tr>\n<td style=\"background-color: #2f89c2;text-align: center\"><b>Factor<\/b><\/td>\n<td style=\"background-color: #2f89c2;text-align: center\"><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">Strain<\/a> Response<\/b><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 373.762px\"><span style=\"font-weight: 400\">Increase <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2689\">Temperature<\/a><\/span><\/td>\n<td style=\"text-align: center;width: 384.238px\"><span style=\"font-weight: 400\">More <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2582\">Ductile<\/a><\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 373.762px\"><span style=\"font-weight: 400\">Increase <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">Strain<\/a> Rate<\/span><\/td>\n<td style=\"text-align: center;width: 384.238px\"><span style=\"font-weight: 400\">More <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2583\">Brittle<\/a><\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 373.762px\"><span style=\"font-weight: 400\">Increase Rock Strength<\/span><\/td>\n<td style=\"text-align: center;width: 384.238px\"><span style=\"font-weight: 400\">More <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2583\">Brittle<\/a><\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-58\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-58\" class=\"h5p-iframe\" data-content-id=\"58\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.2 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4308\" aria-describedby=\"caption-attachment-4308\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.2-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-606\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.2-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4308\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.2 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>9.3\u00a0 Geological Maps <\/strong><\/h2>\n<p><span style=\"font-weight: 400\">Geologic maps are two dimensional (2D) representations of geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formations<\/a> and structures at the Earth&#8217;s surface, including <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formations<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a>, inclined <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a>, and rock types. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">Formations<\/a> are recognizable rock units. Geologists use geologic maps to represent where <\/span>geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formations<\/a><span style=\"font-weight: 400\">, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a>, and inclined rock units are. Geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formations<\/a> are recognizable, mappable rock units. \u00a0Each <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formation<\/a> on the map is indicated by a color and a label.\u00a0\u00a0<\/span>For examples of geologic maps, see the Utah Geological Survey (UGS) <a href=\"http:\/\/geology.utah.gov\/apps\/intgeomap\/\"><i><\/i><span style=\"font-weight: normal !msorm\">geologic map viewer<\/span><i><span style=\"font-weight: normal !msorm\">.<\/span><\/i><\/a><\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">Formation<\/a> labels include symbols that follow a specific protocol. The first one or more letters are uppercase and represent the geologic time <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2192\">period<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formation<\/a>. More than one uppercase letter indicates the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formation<\/a> is associated with multiple time <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2192\">periods<\/a>. The following lowercase letters represent the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formation<\/a> name, abbreviated rock description, or both.<\/p>\n<h3><b>9.3.1 Cross sections<\/b><\/h3>\n<p><span style=\"font-weight: 400\">Cross sections are subsurface interpretations made from surface and subsurface measurements. Maps display geology in the horizontal plane, while cross sections show subsurface geology in the vertical plane. For more information on cross sections, check out the <\/span><span style=\"font-weight: 400\"><a href=\"http:\/\/wiki.aapg.org\/Cross_section\">AAPG wiki<\/a>.<\/span><\/p>\n<h3><b>9.3.2 Strike and Dip<\/b><\/h3>\n<figure id=\"attachment_3350\" aria-describedby=\"caption-attachment-3350\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/StrikeAndDip-e1489776518258.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-607 size-medium\" title=\"Source: Paul Inkenbrandt (created using Trimble SketchUp)\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/StrikeAndDip-e1489776518258-300x247.png\" alt=\"Strike is the line a rock layer would make as it intersects a horizontal plane. Dip is the angle between the horizontal plane and the tilted beds of rock.\" width=\"300\" height=\"247\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/StrikeAndDip-e1489776518258-300x247.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/StrikeAndDip-e1489776518258-65x53.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/StrikeAndDip-e1489776518258-225x185.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/StrikeAndDip-e1489776518258-350x288.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/StrikeAndDip-e1489776518258.png 749w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3350\" class=\"wp-caption-text\">\u201cStrike\u201d and \u201cdip\u201d are words used to describe the orientation of rock layers with respect to North\/South and Horizontal.<\/figcaption><\/figure>\n<figure id=\"attachment_3351\" aria-describedby=\"caption-attachment-3351\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Strike-and-Dip-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-608 size-medium\" title=\"from L. Cameron Mosher\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Strike-and-Dip-1-300x279.jpg\" alt=\"Strike and Dip symbol showing strike of N30E and dip of 45 to the SE.\" width=\"300\" height=\"279\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Strike-and-Dip-1-300x279.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Strike-and-Dip-1-65x60.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Strike-and-Dip-1-225x209.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Strike-and-Dip-1-350x325.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Strike-and-Dip-1.jpg 370w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3351\" class=\"wp-caption-text\">Attitude symbol on geologic map (with compass directions for reference) showing strike of N30oE and dip of 45 to the SE.<\/figcaption><\/figure>\n<p>Geologists use a special symbol called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> to represent inclined <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">beds<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">Strike<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> map symbols look like the capital letter <span style=\"font-style: normal !msorm\"><em>T<\/em><\/span>, with a short trunk and extra-wide top line. The short trunk represents the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> and the top line represents the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">Dip<\/a> is the angle that a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">bed<\/a> plunges into the Earth from the horizontal. A number next to the symbol represents <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> angle. One way to visualize the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> is to think about a line made by standing water on the inclined layer. That line is horizontal and lies on a compass direction that has some angle with respect to true north or south (see figure). The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> angle is that angle measured by a special compass. E.g., N 30\u00b0 E (read north 30 degrees east) means the horizontal line points northeast at an angle of 30\u00b0 from true north. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> symbol is drawn on the map at the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> angle with respect to true north on the map. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> of the inclined layer represents the angle down to the layer from horizontal, in the figure 45<sup>o<\/sup> SE (read dipping 45 degrees to the SE). The direction of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> would be the direction a ball would roll if set on the layer and released. A horizontal rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">bed<\/a> has a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> of 0\u00b0 and a vertical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">bed<\/a> has a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> of 90\u00b0. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">Strike<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> considered together are called <strong>rock attitude<\/strong>.<\/p>\n<p>This video illustrates geologic structures and associated map symbols.<\/p>\n<div class=\"mceTemp\"><\/div>\n<figure id=\"attachment_4297\" aria-describedby=\"caption-attachment-4297\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Fold-Dip-and-Strike-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-609\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fold-Dip-and-Strike-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4297\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Folds, Dip and Strike\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/UzZFMWH-lSQ?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-59\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-59\" class=\"h5p-iframe\" data-content-id=\"59\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.3 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4309\" aria-describedby=\"caption-attachment-4309\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.3-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-610\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.3-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4309\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.3 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>9.4 Folds<\/strong><\/h2>\n<figure id=\"attachment_3352\" aria-describedby=\"caption-attachment-3352\" style=\"width: 398px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Anticline-1-e1490325844690.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-611\" title=\"Source: Paul Inkenbrandt (By Speleotherm (Own work) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons)\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-300x147.png\" alt=\"Model of anticline. Oldest beds are in the center and youngest on the outside. The axial plane intersects the center angle of bend. The hinge line follows the line of greatest bend, where the axial plane intersects the outside of the fold.\" width=\"398\" height=\"195\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-300x147.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-1024x502.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-768x376.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-65x32.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-225x110.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690-350x172.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Anticline-1-e1490325844690.png 1520w\" sizes=\"auto, (max-width: 398px) 100vw, 398px\" \/><\/a><figcaption id=\"caption-attachment-3352\" class=\"wp-caption-text\">Model of anticline. Oldest beds are in the center and youngest on the outside. The axial plane intersects the center angle of bend. The hinge line follows the line of greatest bend, where the axial plane intersects the outside of the fold.<\/figcaption><\/figure>\n<p style=\"text-align: left\">Geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a> are layers of rock that are curved or bent by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1450\">ductile deformation<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">Folds<\/a> are most commonly formed by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compressional<\/a> forces at depth, where hotter temperatures and higher <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2917\">confining<\/a> pressures allow <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1450\">ductile deformation<\/a> to occur.<\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">Folds<\/a> are described by the orientation of their axes, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial planes<\/a>, and limbs. The plane that splits the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> into two halves is known as the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial plane<\/a><\/strong>. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">fold axis<\/a><\/strong> is the line along which the bending occurs and is where the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial plane<\/a> intersects the folded <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a>. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">hinge line<\/a><\/strong> follows the line of greatest bend in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a>. The two sides of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> are the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> <strong>limbs<\/strong>.<\/p>\n<p><strong>Symmetrical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a><\/strong> have a vertical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial plane<\/a> and limbs have equal but opposite dips. <strong>Asymmetrical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a><\/strong> have dipping, non-vertical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial planes<\/a>, where the limbs <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> at different angles. <strong>Overturned <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a><\/strong> have steeply dipping <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial planes<\/a> and the limbs <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> in the same direction but usually at different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> angles. <strong>Recumbent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a><\/strong> have horizontal or nearly horizontal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial planes<\/a>. When the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axis<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> plunges into the ground, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> is called a <strong>plunging <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a><\/strong>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">Folds<\/a> are classified into five categories: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1457\">anticline<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1458\">syncline<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1459\">monocline<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">dome<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">basin<\/a>.<\/p>\n<h3><b>9.4.1 Anticline<\/b><\/h3>\n<figure id=\"attachment_3353\" aria-describedby=\"caption-attachment-3353\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/17177576122_b63f2ee137_o.jpg\" target=\"_blank\" rel=\"https:\/\/www.flickr.com\/photos\/utahgeologicalsurvey\/17177576122\/ noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-612 size-medium\" title=\"Source: Utah Geological Survey https:\/\/www.flickr.com\/photos\/utahgeologicalsurvey\/17177576122\/\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/17177576122_b63f2ee137_o-300x237.jpg\" alt=\"Oblique aerial photograph of an anticline in Utah. The rock beds are dipping in opposite directions on either side of the anticline's axis.\" width=\"300\" height=\"237\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/17177576122_b63f2ee137_o-300x237.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/17177576122_b63f2ee137_o-65x51.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/17177576122_b63f2ee137_o-225x177.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/17177576122_b63f2ee137_o-350x276.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/17177576122_b63f2ee137_o.jpg 700w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3353\" class=\"wp-caption-text\">Oblique view of the Virgin Anticline (bottom right of photo) looking north. The anticline is plunging into the ground to the north. Units from youngest to oldest Jn = Jurassic Navajo Sandstone; Jk = Jurassic Kayenta Formation; Trc = Triassic Chinle Formation; Trm = Triassic Moenkopi; Pk = Permian Kaibab Formation.<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1457\">Anticlines<\/a> are arch-like, or <span style=\"font-style: normal !msorm\">A<\/span>-shaped, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a> that are convex-upward in shape. They have downward curving limbs and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">beds<\/a> that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> down and away from the central <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">fold axis<\/a>. In <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1457\">anticlines<\/a>, the oldest rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a> are in the center of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a>, along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axis<\/a>, and the younger <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">beds<\/a> are on the outside. Since geologic maps show the intersection of surface topography with underlying geologic structures, an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1457\">anticline<\/a> on a geologic map can be identified by both the attitude of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a> forming the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> and the older age of the rocks inside the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a>. An <strong>antiform<\/strong> has the same shape as an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1457\">anticline<\/a>, but the relative ages of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">beds<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> cannot be determined. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3338\">Oil<\/a> geologists are interested in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1457\">anticlines<\/a> because they can form <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3338\">oil<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3342\">traps<\/a>, where <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3338\">oil<\/a> migrates up along the limbs of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> and accumulates in the high point along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">fold axis<\/a>.<\/p>\n<h3><b>9.4.2 Syncline<\/b><\/h3>\n<div class=\"sketchfab-embed-wrapper\">\n<p><iframe loading=\"lazy\" id=\"oembed-2\" class=\"wp-embedded-content\" sandbox=\"allow-scripts\" title=\"Synclinal fold - Macigno Formation\" width=\"500\" height=\"281\" src=\"https:\/\/sketchfab.com\/models\/3f0259ea2c6b4807a32fe3c950d13324\/embed#?secret=AgL5oPloWo\" data-secret=\"AgL5oPloWo\" frameborder=\"0\"><\/iframe><\/p>\n<p style=\"font-size: 13px;font-weight: normal;margin: 5px;color: #4a4a4a;text-align: center\"><a style=\"font-weight: bold;color: #1caad9\" href=\"https:\/\/sketchfab.com\/models\/3f0259ea2c6b4807a32fe3c950d13324?utm_medium=embed&amp;utm_source=website&amp;utm_campain=share-popup\" target=\"_blank\" rel=\"noopener noreferrer\">Synclinal fold &#8211; Macigno Formation<\/a><br \/>\nby <a style=\"font-weight: bold;color: #1caad9\" href=\"https:\/\/sketchfab.com\/alanpitts?utm_medium=embed&amp;utm_source=website&amp;utm_campain=share-popup\" target=\"_blank\" rel=\"noopener noreferrer\">alanpitts<\/a> on <a style=\"font-weight: bold;color: #1caad9\" href=\"https:\/\/sketchfab.com?utm_medium=embed&amp;utm_source=website&amp;utm_campain=share-popup\" target=\"_blank\" rel=\"noopener noreferrer\">Sketchfab<\/a><\/p>\n<figure id=\"attachment_4303\" aria-describedby=\"caption-attachment-4303\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Synclinal-Fold-Element-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-613\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Synclinal-Fold-Element-QR-Code.png 1160w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4303\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this interactive activity via this QR Code.<\/figcaption><\/figure>\n<\/div>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1458\">Synclines<\/a> are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3183\">trough<\/a>-like, or U shaped, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a> that are concave-upward in shape. They have <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">beds<\/a> that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> down and in toward the central <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">fold axis<\/a>. In <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1458\">synclines<\/a>, older rock is on the outside of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> and the youngest rock is inside of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">fold axis<\/a>. A <strong>synform<\/strong> has the shape of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1458\">syncline<\/a> but like an antiform, does not have distinguishable age zones.<\/p>\n<h3><b>9.4.3 Monocline<\/b><\/h3>\n<figure id=\"attachment_3354\" aria-describedby=\"caption-attachment-3354\" style=\"width: 403px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/monocline-example.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-614\" title=\"Source: Utah Geological Survey https:\/\/www.flickr.com\/photos\/utahgeologicalsurvey\/16596756273\/\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-300x221.jpg\" alt=\"Oblique aerial photograph of a long line of multicolored rock beds dipping into the ground. The beds are fractured and erode in a way that makes the parts sticking out look like triangles.\" width=\"403\" height=\"297\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-300x221.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-1024x756.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-768x567.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-1536x1134.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-65x48.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-225x166.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example-350x258.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/monocline-example.jpg 1600w\" sizes=\"auto, (max-width: 403px) 100vw, 403px\" \/><\/a><figcaption id=\"caption-attachment-3354\" class=\"wp-caption-text\">Oblique aerial photograph of Capitol Reef National Park&#8217;s Water Pocket fold. The perspective is looking southwest toward 50-Mile Mountain and Navajo Mountain.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1459\">Monoclines<\/a><\/strong> are step-like <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">folds<\/a>, in which flat rocks are upwarped or downwarped, then continue flat. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1459\">Monoclines<\/a> are relatively common on the Colorado Plateau where they form \u201c<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2898\">reefs<\/a>,\u201d which are ridges that act as topographic barriers and should not be confused with ocean <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2898\">reefs<\/a> (see\u00a0<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>). Capitol <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2898\">Reef<\/a> is an example of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1459\">monocline<\/a> in Utah. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1459\">Monoclines<\/a> can be caused by bending of shallower sedimentary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a> as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> grow below them. These <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> are commonly called &#8220;blind <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a>&#8221; because they end before reaching the surface and can be either normal or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3073\">reverse faults<\/a>.<\/span><\/p>\n<h3><b>9.4.4 Dome<\/b><\/h3>\n<figure id=\"attachment_3355\" aria-describedby=\"caption-attachment-3355\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/swell-dome-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3355 size-medium\" title=\"From NASA. https:\/\/eol.jsc.nasa.gov\/SearchPhotos\/photo.pl?mission=ISS006&amp;amp;roll=E&amp;amp;frame=31497\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/swell-dome-scaled-1.jpg\" alt=\"View of a dome in Utah from space. The photo shows upwarped beds of rock, where the center of the dome has been eroded away.\" width=\"300\" height=\"204\" \/><\/a><figcaption id=\"caption-attachment-3355\" class=\"wp-caption-text\">View of the San Rafael Swell from space. In this photograph, north is to the left. Dipping beds of rock will have lines of shadow around them. Note that the center part of the dome is eroded away.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">A <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">dome<\/a> is a symmetrical to semi-symmetrical upwarping of rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">beds<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">Domes<\/a> have a shape like an inverted bowl, similar to an architectural <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">dome<\/a> on a building. Examples of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">domes<\/a> in Utah include the San Rafael Swell, Harrisburg Junction <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">Dome<\/a>, and Henry Mountains<\/span><span style=\"font-weight: 400\">. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">Domes<\/a> are formed from compressional forces, underlying <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2675\">igneous<\/a> intrusions<\/span><span style=\"font-weight: 400\"> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>), by salt diapirs, or even impacts, like upheaval <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">dome<\/a> in Canyonlands National Park.<\/span><\/p>\n<h3><b>9.4.5 Basin<\/b><\/h3>\n<figure id=\"attachment_3356\" aria-describedby=\"caption-attachment-3356\" style=\"width: 201px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.4_Denver_Basin_Location_Map.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-616\" title=\"By Daniel H. Knepper, Jr. (editor), US Geological Survey (http:\/\/pubs.usgs.gov\/circ\/c1219\/) [Public domain], via Wikimedia Commons https:\/\/commons.wikimedia.org\/wiki\/File:Denver_Basin_Location_Map.png\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map-184x300.png\" alt=\"Schematic map of the Denver Basin, a sedimentary basin under Denver Colorado. The map includes a cross section of the area, showing beds arching into a syncline.\" width=\"201\" height=\"328\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map-184x300.png 184w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map-627x1024.png 627w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map-65x106.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map-225x368.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map-350x572.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.4_Denver_Basin_Location_Map.png 750w\" sizes=\"auto, (max-width: 201px) 100vw, 201px\" \/><\/a><figcaption id=\"caption-attachment-3356\" class=\"wp-caption-text\">The Denver Basin is an active sedimentary basin at the eastern extent of the Rocky Mountains. As sediment accumulates, the basin subsides, creating a basin-shape of beds that are all dipping towards the center of the basin.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">A <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">basin<\/a> is the inverse of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1460\">dome<\/a>, a bowl-shaped depression in a rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2858\">bed<\/a>. The Uinta <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">Basin<\/a> in Utah is an example of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">basin<\/a>. Some structural basins are also <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1463\">sedimentary basins<\/a> that collect large quantities of sediment over time. Sedimentary basins can form as a result of folding but are much more commonly produced in mountain building, forming between mountain blocks or via <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faulting<\/a>. Regardless of the cause, as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">basin<\/a> sinks or subsides, it can accumulate more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediment<\/a>\u00a0because the weight of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediment<\/a> causes more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1464\">subsidence<\/a> in a positive-feedback loop. There are active <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1463\">sedimentary basins<\/a> all over the world<\/span>. An example of a rapidly subsiding <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">basin<\/a> in Utah is the Oquirrh <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">Basin<\/a>, dated to the Pennsylvanian-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1428\">Permian<\/a> age, which has accumulated over 9,144 m (30,000 ft) of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2852\">fossiliferous<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2834\">sandstones<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2839\">shales<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2851\">limestones<\/a>. These <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a> can be seen in the Wasatch Mountains along the east side of Utah Valley, especially on Mt. Timpanogos and in Provo Canyon.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-60\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-60\" class=\"h5p-iframe\" data-content-id=\"60\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.4 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4310\" aria-describedby=\"caption-attachment-4310\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.4-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-617\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.4-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4310\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.4 via this QR Code.<\/figcaption><\/figure>\n<h2>9.5 Faults<\/h2>\n<figure id=\"attachment_3357\" aria-describedby=\"caption-attachment-3357\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/normfaultLABEL.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-618 size-full\" title=\"Source: USGS https:\/\/geomaps.wr.usgs.gov\/parks\/deform\/normfaultLABEL.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/normfaultLABEL.gif\" alt=\"Block diagram of a normal fault.\" width=\"300\" height=\"172\" \/><\/a><figcaption id=\"caption-attachment-3357\" class=\"wp-caption-text\">Common terms used for normal faults. Normal faults form when the hanging wall move down relative to the footwall.<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Faults<\/a> are the places in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a> where <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">brittle deformation<\/a> occurs as two blocks of rocks move relative to one another. Normal and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3073\">reverse faults<\/a> display vertical, also known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3066\">dip-slip<\/a>, motion. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3066\">Dip-slip<\/a> motion consists of relative up-and-down movement along a dipping <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> between two blocks, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3067\">hanging wall<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3068\">footwall<\/a>. In a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3066\">dip-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2664\">system<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3068\">footwall<\/a> is below the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3067\">hanging wall<\/a> is above the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane. A good way to remember this is to imagine a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3324\">mine<\/a> tunnel running along a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a>; the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3067\">hanging wall<\/a> would be where a miner would hang a lantern and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3068\">footwall<\/a> would be at the miner\u2019s feet.<\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Faulting<\/a> as a term refers to rupture of rocks. Such ruptures occur at <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries but can also occur in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> interiors as well. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Faults<\/a> slip along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3107\">fault scarp<\/a> is the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3081\">offset<\/a> of the surface produced where the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> breaks through the surface. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3069\">Slickensides<\/a> are polished, often grooved surfaces along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane created by friction during the movement.<\/p>\n<p>A <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1934\">joint<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1934\">fracture<\/a> is a plane of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">brittle deformation<\/a> in rock created by movement that is not <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3081\">offset<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1447\">sheared<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1934\">Joints<\/a> can result from many processes, such as cooling, depressurizing, or folding. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1934\">Joint<\/a> systems may be regional affecting many square miles.<\/p>\n<h3>9.5.1 Normal Faults<\/h3>\n<p>Normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> move by a vertical motion where the hanging-wall moves downward relative to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3068\">footwall<\/a> along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a>. Normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> are created by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">tensional<\/a> forces in the crust. Normal faults and tensional forces commonly occur at <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2599\">divergent<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries, where the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a> is being stretched by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">tensional<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">stresses<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). Examples of normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> in Utah are the Wasatch <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a>, the Hurricane <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a>, and other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> bounding the valleys in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a> province.<\/p>\n<figure id=\"attachment_3358\" aria-describedby=\"caption-attachment-3358\" style=\"width: 418px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-300x199-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-619\" title=\"James St. John https:\/\/commons.wikimedia.org\/wiki\/File:Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01.jpg Pennsylvanian Honaker Trail Formation\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-300x199-1.jpg\" alt=\"Roadcut outcrop of multicolor rock beds offset by a normal fault.\" width=\"418\" height=\"277\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-300x199-1.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-300x199-1-65x43.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Faults_in_Moenkopi_Formation_Moab_Canyon_Utah_USA_01-300x199-1-225x149.jpg 225w\" sizes=\"auto, (max-width: 418px) 100vw, 418px\" \/><\/a><figcaption id=\"caption-attachment-3358\" class=\"wp-caption-text\">Example of a normal fault in an outcrop of the Pennsylvanian Honaker Trail Formation near Moab, Utah.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3359\" aria-describedby=\"caption-attachment-3359\" style=\"width: 351px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Horst-Graben.svg_.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3359\" title=\"By Horst_graben.jpg: U.S. Geological Survey derivative work: Gregors (talk) 11:17, 7 June 2011 (UTC) (Horst_graben.jpg) [Public domain], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Horst-Graben.svg_-1.png\" alt=\"While the area extends, individual grabens drop down relative to the horsts.\" width=\"351\" height=\"180\" \/><\/a><figcaption id=\"caption-attachment-3359\" class=\"wp-caption-text\">Faulting that occurs in the crust under tensional stress.<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2626\">Grabens<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2625\">horsts<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3071\">half-grabens<\/a> are blocks of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a> or rock bounded by normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2626\">Grabens<\/a> drop down relative to adjacent blocks and create valleys. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2625\">Horsts<\/a> rise up relative to adjacent down-dropped blocks and become areas of higher topography. Where occurring together, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2625\">horsts<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2626\">grabens<\/a> create a symmetrical pattern of valleys surrounded by normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> on both sides and mountains. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3071\">Half-grabens<\/a> are a one-sided version of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2625\">horst<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2626\">graben<\/a>, where blocks are tilted by a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3070\">normal fault<\/a> on one side, creating an asymmetrical valley-mountain arrangement. The mountain-valleys of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a> Province of Western Utah and Nevada consist of a series of full and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3071\">half-grabens<\/a> from the Salt Lake Valley to the Sierra Nevada Mountains.<\/p>\n<p>Normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> do not continue clear into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2586\">mantle<\/a>.\u00a0 In the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a> Province, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3070\">normal fault<\/a> tends to decrease with depth, i.e., the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> angle becomes shallower and more horizontal as it goes deeper. Such decreasing dips happen when large amounts of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">extension<\/a> occur along very low-angle normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a>, known as <strong>detachment <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a><\/strong>. The normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a>, produced by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">tension<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a>, appear to become detachment <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> at greater depths.<\/p>\n<h3>9.5.2 Reverse Faults<\/h3>\n<figure id=\"attachment_3360\" aria-describedby=\"caption-attachment-3360\" style=\"width: 290px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/reversefaultLABEL.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-621 size-full\" title=\"Source: USGS https:\/\/geomaps.wr.usgs.gov\/parks\/deform\/reversefaultLABEL.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/reversefaultLABEL.gif\" alt=\"Block diagram of a thrust fault, where the hangingwall overlies the footwall.\" width=\"290\" height=\"157\" \/><\/a><figcaption id=\"caption-attachment-3360\" class=\"wp-caption-text\">Simplified block diagram of a reverse fault.<\/figcaption><\/figure>\n<p>In <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3073\">reverse faults<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compressional<\/a> forces cause the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3067\">hanging wall<\/a> to move up relative to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3068\">footwall<\/a>. A <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3074\">thrust fault<\/a> is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3073\">reverse fault<\/a> where the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane has a low <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> angle of less than 45\u00b0. Thrust <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> carry older rocks on top of younger rocks and can even cause repetition of rock units in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2859\">stratigraphic<\/a> record.<\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2600\">Convergent<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subduction<\/a> zones create a special type of \u201creverse\u201d <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3075\">megathrust<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> where denser <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2581\">oceanic crust<\/a> drives down beneath less dense overlying <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3075\">Megathrust<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> cause the largest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> earthquakes yet measured and commonly cause <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1933\">massive<\/a> destruction and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a>.<\/p>\n<figure id=\"attachment_3361\" aria-describedby=\"caption-attachment-3361\" style=\"width: 317px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/1280px-Thrust_system_en.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-622\" title=\"Source: USGS https:\/\/geomaps.wr.usgs.gov\/parks\/deform\/reversefaultLABEL.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-300x124.jpg\" alt=\"Block diagram of a thrust fault, where the hangingwall overlies the footwall.\" width=\"317\" height=\"131\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-300x124.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-1024x423.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-768x317.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-65x27.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-225x93.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en-350x145.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1280px-Thrust_system_en.jpg 1280w\" sizes=\"auto, (max-width: 317px) 100vw, 317px\" \/><\/a><figcaption id=\"caption-attachment-3361\" class=\"wp-caption-text\">Terminology of thrust faults (low-angle reverse faults). A klippe is the remnant of the hangingwall (aka nappe), where the surrounding material has been eroded away. A window is where part of the hangingwall has been eroded away to expose the footwall (autochton). Note the symbol shows flags on the overlying thrust plate.<\/figcaption><\/figure>\n<figure id=\"attachment_3362\" aria-describedby=\"caption-attachment-3362\" style=\"width: 357px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/814080386_b34c44cfe6_z.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-623\" title=\"Photo by Ron Schott:\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/814080386_b34c44cfe6_z.jpg\" alt=\"Beds of rock offset along a fault plane to where one section of the rock has been pushed up over itself.\" width=\"357\" height=\"238\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/814080386_b34c44cfe6_z.jpg 640w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/814080386_b34c44cfe6_z-300x200.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/814080386_b34c44cfe6_z-65x43.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/814080386_b34c44cfe6_z-225x150.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/814080386_b34c44cfe6_z-350x233.jpg 350w\" sizes=\"auto, (max-width: 357px) 100vw, 357px\" \/><\/a><figcaption id=\"caption-attachment-3362\" class=\"wp-caption-text\">Ketobe Knob in the San Rafael Swell of Utah displays an example of a thrust fault.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<h3>9.5.3\u00a0 Strike-slip Faults<\/h3>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">Strike-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> have side-to-side motion. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">Strike-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> are most commonly associated with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries and are prevalent in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1934\">fracture<\/a> zones along <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2630\">mid-ocean ridges<\/a>. In pure <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">strike-slip<\/a> motion, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> blocks on either side of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> do not move up or down relative to each other, rather move laterally, side to side. The direction of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">strike-slip<\/a> movement is determined by an observer standing on a block on one side of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a>. If the block on the opposing side of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> moves left relative to the observer\u2019s block, this is called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2632\">sinistral<\/a> motion. If the opposing block moves right, it is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3077\">dextral<\/a> motion.<\/p>\n<p>Video showing motion in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">strike-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a>.<\/p>\n<p>&nbsp;<\/p>\n<div style=\"width: 1920px;\" class=\"wp-video\"><video class=\"wp-video-shortcode\" id=\"video-667-1\" width=\"1920\" height=\"1080\" preload=\"metadata\" controls=\"controls\"><source type=\"video\/mp4\" src=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/strikeslip.mp4?_=1\" \/><a href=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/strikeslip.mp4\">http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/strikeslip.mp4<\/a><\/video><\/div>\n<figure id=\"attachment_4312\" aria-describedby=\"caption-attachment-4312\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.5-Video-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-624\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Video-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4312\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this interactive activity via this QR Code.<\/figcaption><\/figure>\n<p>Bends along <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">strike-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> create areas of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compression<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">tension<\/a> between the sliding blocks (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">Tensional<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stresses<\/a> create transtensional features with normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> and basins, such as the Salton Sea in California. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">Compressional<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stresses<\/a> create <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2634\">transpressional<\/a> features with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3073\">reverse faults<\/a> and cause small-scale mountain building, such as the San Gabriel Mountains in California. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> that splay off <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2634\">transpression<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2635\">transtension<\/a> features are known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3078\">flower structures<\/a>.<\/p>\n<figure id=\"attachment_3363\" aria-describedby=\"caption-attachment-3363\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.5_Flowerstructure1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-625\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1-300x173.png\" alt=\"Block diagrams of mountains or basins in flower structures.\" width=\"300\" height=\"173\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1-300x173.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1-768x444.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1-65x38.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1-225x130.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1-350x202.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5_Flowerstructure1.png 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3363\" class=\"wp-caption-text\">Flower structures created by strike-slip faults. Depending on the relative movement in relation to the bend in the fault, flower structures can create basins or mountains.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">An example of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3077\">dextral<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3077\">right-lateral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">strike-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> is the San Andreas <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a>, which denotes a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a> boundary between the North American and Pacific <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plates<\/a>. An example of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2632\">sinistral<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2632\">left-lateral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">strike-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> is the Dead Sea <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> in Jordan and Israel.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p>Video showing how <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> are classified.<\/p>\n<figure id=\"attachment_4320\" aria-describedby=\"caption-attachment-4320\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Classification-of-Faults-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-626\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Classification-of-Faults-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4320\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-3\" title=\"Classification of Faults\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/qlk7IfYMufs?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-61\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-61\" class=\"h5p-iframe\" data-content-id=\"61\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.5 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4311\" aria-describedby=\"caption-attachment-4311\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.5-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-627\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.5-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4311\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.5 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>9.6 Earthquake Essentials<\/strong><\/h2>\n<p><span style=\"font-weight: 400\">Earthquakes are felt at the surface of the Earth when energy is released by blocks of rock sliding past each other, i.e. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faulting<\/a> has occurred. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">Seismic energy<\/a> thus released travels through the Earth in the form of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves. <\/span>Most earthquakes occur along active <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">Intraplate<\/a> earthquakes (not along <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries) occur and are still poorly understood. The\u00a0<a href=\"http:\/\/earthquake.usgs.gov\/earthquakes\/map\/#%7B%22feed%22%3A%227day_all%22%2C%22search%22%3Anull%2C%22listFormat%22%3A%22default%22%2C%22sort%22%3A%22newest%22%2C%22basemap%22%3A%22grayscale%22%2C%22autoUpdate%22%3Atrue%2C%22restrictListToMap%22%3Atrue%2C%22timeZone%22%3A%22utc%22%2C%22mapposition%22%3A%5B%5B32.93492866908233%2C-125.88134765625%5D%2C%5B47.97521412341618%2C-104.32617187499999%5D%5D%2C%22overlays%22%3A%7B%22plates%22%3Atrue%7D%2C%22viewModes%22%3A%7B%22map%22%3Atrue%2C%22list%22%3Atrue%2C%22settings%22%3Atrue%2C%22help%22%3Afalse%7D%7D\">USGS Earthquakes Hazards Program<\/a>\u00a0has a real time map showing the most recent earthquakes..<\/p>\n<h3><b>9.6.1 How Earthquakes Happen<\/b><\/h3>\n<figure id=\"attachment_3364\" aria-describedby=\"caption-attachment-3364\" style=\"width: 425px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/elastic-deformation-and-rupture-1024x531-1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-628\" title=\"Steven Earle\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1-300x156.png\" alt=\"Process of elastic rebound: a) Undeformed state, b) accumulation of elastic strain, and c) brittle failure and release of elastic strain.\" width=\"425\" height=\"220\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1-300x156.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1-768x398.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1-65x34.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1-225x117.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1-350x181.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/elastic-deformation-and-rupture-1024x531-1.png 1024w\" sizes=\"auto, (max-width: 425px) 100vw, 425px\" \/><\/a><figcaption id=\"caption-attachment-3364\" class=\"wp-caption-text\">Process of elastic rebound: a) Undeformed state, b) accumulation of elastic strain, and c) brittle failure and release of elastic strain.<\/figcaption><\/figure>\n<p>The release of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic energy<\/a> is explained by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3079\">elastic rebound<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2655\">theory<\/a>. When rock is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strained<\/a> to the point that it undergoes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">brittle deformation<\/a>, The place where the initial offsetting rupture takes place between the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> blocks is called the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3081\">offset<\/a> propagates along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a>, which is known as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane.<\/p>\n<p>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> blocks of persistent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> like the Wasatch <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a> (Utah), that show recurring movements, are locked together by friction. Over hundreds to thousands of years, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> builds up along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> until it overcomes frictional resistance, rupturing the rock and initiating <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> movement. The deformed unbroken rocks snap back toward their original shape in a process called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3079\">elastic rebound<\/a><b>.<\/b> Think of bending a stick until it breaks; stored energy is released, and the broken pieces return to near their original orientation.<\/p>\n<p>Bending, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1450\">ductile deformation<\/a> of the rocks near a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a>, reflects a build-up of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a>. In earthquake-prone areas like California, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> gauges are used to measure this bending and help seismologists, scientists who study earthquakes, understand more about predicting them. In locations where the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> is not locked, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> causes continuous, gradual displacement between the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> blocks called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2447\">creep<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2447\">creep<\/a> occurs along some parts of the San Andreas <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a> (California).<\/p>\n<p>After an initial earthquake, continuous application of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a> causes elastic energy to begin to build again during a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2192\">period<\/a> of inactivity along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a>. The accumulating elastic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> may be periodically released to produce small earthquakes on or near the main <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3082\">foreshocks<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3082\">Foreshocks<\/a> can occur hours or days before a large earthquake, or may not occur at all. The main release of energy during the major earthquake is known as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3083\">mainshock<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3084\">Aftershocks<\/a> may follow the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3083\">mainshock<\/a> to adjust new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> produced during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> movement and generally decrease over time.<\/p>\n<h3><b>9.6.2 Focus and Epicenter<\/b><\/h3>\n<figure id=\"attachment_3365\" aria-describedby=\"caption-attachment-3365\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Epicenter_Diagram.svg_.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-629 size-medium\" title=\"By Rostik252004 (Own work, based on File:Epicenter Diagram.svg) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Epicenter_Diagram.svg_-300x233.png\" alt=\"The hypocenter is the point from which seismic energy emanates. The epicenter is the point on land surface vertically above the hypocenter.\" width=\"300\" height=\"233\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Epicenter_Diagram.svg_-300x233.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Epicenter_Diagram.svg_-65x50.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Epicenter_Diagram.svg_-225x175.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Epicenter_Diagram.svg_-350x272.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Epicenter_Diagram.svg_.png 576w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3365\" class=\"wp-caption-text\">The hypocenter is the point along the fault plane in the subsurface from which seismic energy emanates. The epicenter is the point on land surface vertically above the hypocenter.<\/figcaption><\/figure>\n<p style=\"text-align: left\">The earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>, also called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">hypocenter<\/a><\/strong>, is the initial point of rupture and displacement of the rock moves from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">hypocenter<\/a> along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> surface. The earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">hypocenter<\/a> is the point along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane from which initial <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves spread outward and is always at some depth below the ground surface. From the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>, rock displacement propagates up, down, and laterally along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane. This displacement produces shock waves called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves.\u00a0 The larger the displacement between the opposing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> blocks and the further the displacement propagates along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> surface, the more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic energy<\/a> is released and the greater the amount and time of shaking is produced. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a> is the location on the Earth\u2019s surface vertically above the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>. This is the location that most news reports give because it is the center of the area where people are affected.<\/p>\n<h3><b>9.6.3 Seismic Waves<\/b><\/h3>\n<p>To understand earthquakes and how earthquake energy moves through the Earth, consider the basic properties of waves. Waves describe how energy moves through a medium, such as rock or unconsolidated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediments<\/a> in the case of earthquakes. Wave <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a> indicates the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> or height of earthquake motion. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3186\">Wavelength<\/a> is the distance between two successive peaks of a wave. Wave frequency is the number of repetitions of the motion over a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2192\">period<\/a> of time, cycles per time unit. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2192\">Period<\/a>, which is the amount of time for a wave to travel one <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3186\">wavelength<\/a>, is the inverse of frequency. When multiple waves combine, they can interfere with each other (see figure). When waves combine in sync, they produce constructive interference, where the influence of one wave adds to and magnifies the other. If waves are out of sync, they produce destructive interference, which diminishes the amplitudes of both waves. If two combined waves have the same <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a> and frequency but are one-half <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3186\">wavelength<\/a> out of sync, the resulting destructive interference can eliminate each wave. These processes of wave <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a>, frequency, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2192\">period<\/a>, and constructive and destructive interference determine the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> and intensity of earthquakes.<\/p>\n<figure id=\"attachment_3366\" aria-describedby=\"caption-attachment-3366\" style=\"width: 690px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Waventerference.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-630\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Waventerference.gif\" alt=\"When two waves interact, they can increase or decrease each others amplitude depending on if they are aligned\" width=\"690\" height=\"295\" \/><\/a><figcaption id=\"caption-attachment-3366\" class=\"wp-caption-text\">Example of constructive and destructive interference; note red line representing the results of interference.<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">Seismic<\/a> waves are the physical expression of energy released by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3079\">elastic rebound<\/a> of rock within displaced <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> blocks and are felt as an earthquake. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">Seismic<\/a> waves occur as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3088\">body waves<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3088\">Body waves<\/a> pass underground through the Earth\u2019s interior body and are the first <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves to propagate out from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>. Body waves include primary (P) waves and secondary (S) waves. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P waves<\/a> are the fastest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3088\">body waves<\/a> and move through rock via <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compression<\/a>, very much like sound waves move through air. Rock particles move forward and back during passage of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P waves<\/a>, enabling them to travel through solids, liquids, plasma, and gases. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3090\">S waves<\/a> travel slower, following <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P waves<\/a>, and propagate as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1447\">shear<\/a> waves that move rock particles from side to side. Because they are restricted to lateral movement, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3090\">S waves<\/a> can only travel through solids but not liquids, plasma, or gases.<\/p>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Onde_compression_impulsion_1d_30_petit.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-631 aligncenter\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Onde_compression_impulsion_1d_30_petit.gif\" alt=\"P-waves are compressional.\" width=\"461\" height=\"349\" \/><\/a><\/p>\n<p style=\"text-align: center\"><em><span style=\"font-size: 10pt\">P-waves are compressional<\/span>.<\/em><\/p>\n<figure id=\"attachment_3369\" aria-describedby=\"caption-attachment-3369\" style=\"width: 476px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Onde_cisaillement_impulsion_1d_30_petit.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-632\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Onde_cisaillement_impulsion_1d_30_petit.gif\" alt=\"S waves are shear.\" width=\"476\" height=\"361\" \/><\/a><figcaption id=\"caption-attachment-3369\" class=\"wp-caption-text\">S waves are shear.<\/figcaption><\/figure>\n<p>During an earthquake, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3088\">body waves<\/a> pass through the Earth and into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2586\">mantle<\/a> as a sub-spherical wave front. Considering a point on a wave front, the path followed by a specific point on the spreading wave front is called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> ray and a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> ray reaches a specific <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismograph<\/a> located at one of thousands of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> monitoring stations scattered over the Earth. D<span style=\"font-weight: 400\">ensity increases with depth in the Earth, and since <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> velocity increases with density, a process called <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3091\">refraction<\/a><\/b><span style=\"font-weight: 400\"> causes earthquake rays to curve away from the vertical and bend back toward the surface, passing through different bodies of rock along the way.<\/span><\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">Surface waves<\/a> are produced when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3088\">body waves<\/a> from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> the Earth\u2019s surface. Surface waves travel along the Earth&#8217;s surface, radiating outward from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a>.\u00a0 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">Surface waves<\/a> take the form of rolling waves called <a href=\"https:\/\/www.youtube.com\/watch?v=6yXgfYHAS7c\">Raleigh Waves<\/a> and side to side waves called <a href=\"https:\/\/www.youtube.com\/watch?v=t7wJu0Kts7w\">Love Waves<\/a> (watch videos for wave propagation animations). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">Surface waves<\/a> are produced primarily as the more energetic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3090\">S waves<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> the surface from below with some <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface wave<\/a> energy contributed by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P waves<\/a> (videos courtesy <a href=\"http:\/\/blog.Wolfram.com\">blog.Wolfram.com<\/a>). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">Surface waves<\/a> travel more slowly than <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3088\">body waves<\/a> and because of their complex horizontal and vertical movement, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a> are responsible for most of the damage caused by an earthquake. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3092\">Love waves<\/a> produce predominantly horizontal ground shaking and, ironically from their name, are the most destructive. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3093\">Rayleigh waves<\/a> produce an elliptical motion with longitudinal dilation and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compression<\/a>, like ocean waves. However, Raleigh waves cause rock particles to move in a direction opposite to that of water particles in ocean waves.<\/p>\n<p>The Earth has been described as ringing like a bell after an earthquake with earthquake energy reverberating inside it.\u00a0 Like other waves, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves refract (bend) and bounce (reflect) when passing through rocks of differing densities.\u00a0 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3090\">S waves<\/a>, which cannot move through liquid, are blocked by the Earth&#8217;s liquid <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2595\">outer core<\/a>, creating an S wave shadow zone on the side of the planet opposite to the earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P waves<\/a>, on the other hand, pass through the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2589\">core<\/a>, but are refracted into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2589\">core<\/a> by the difference of density at the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2589\">core<\/a>&#8211;<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2586\">mantle<\/a> boundary. This has the effect of creating a cone shaped <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P wave<\/a> shadow zone on parts of the other side of the Earth from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>.<\/p>\n<p><iframe loading=\"lazy\" id=\"oembed-4\" title=\"2011 Tohoku Earthquake, Mag. 9.0. Body and Surface Waves\" src=\"https:\/\/player.vimeo.com\/video\/153300296?dnt=1&amp;app_id=122963\" width=\"500\" height=\"375\" frameborder=\"0\"><\/iframe><\/p>\n<p style=\"text-align: center\"><span style=\"font-size: 10pt\"><em><a href=\"https:\/\/vimeo.com\/153300296\">2011 Tohoku Earthquake, Mag. 9.0. Body and Surface Waves<\/a> from <a href=\"https:\/\/vimeo.com\/seismicsoundlab\">seismicsoundlab<\/a> on <a href=\"https:\/\/vimeo.com\">Vimeo<\/a>.<\/em><\/span><\/p>\n<figure id=\"attachment_4292\" aria-describedby=\"caption-attachment-4292\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/2011-Tohoku-Earthquake-Vimeo-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-633\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/2011-Tohoku-Earthquake-Vimeo-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4292\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this Vimeo video via this QR Code.<\/figcaption><\/figure>\n<h3>9.6.4 Induced Seismicity<\/h3>\n<figure id=\"attachment_2493\" aria-describedby=\"caption-attachment-2493\" style=\"width: 334px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Cumulative_induced_seismicity.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-61\" title=\"USGS, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-300x228.png\" alt=\"There is a large spike in earthquakes\" width=\"334\" height=\"254\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-300x228.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-1024x779.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-768x584.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-65x49.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-225x171.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity-350x266.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cumulative_induced_seismicity.png 1112w\" sizes=\"auto, (max-width: 334px) 100vw, 334px\" \/><\/a><figcaption id=\"caption-attachment-2493\" class=\"wp-caption-text\">Frequency of earthquakes in the central United States. Note the sharp increase in the number of earthquakes from 2010 to 2015.<\/figcaption><\/figure>\n<p>Earthquakes known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3109\">induced seismicity<\/a> occur near <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3339\">natural gas<\/a> extraction sites because of human activity. Injection of waste fluids in the ground, commonly a byproduct of an extraction process for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3339\">natural gas<\/a> known as <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3108\">fracking<\/a><\/strong>, can increase the outward pressure that liquid in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3116\">pores<\/a> of a rock exerts, known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3116\">pore<\/a> pressure.\u00a0 The increase in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3116\">pore<\/a> pressure decreases the frictional forces that keep rocks from sliding past each other, essentially lubricating <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> planes. <span style=\"font-weight: 400\">This effect is causing earthquakes to occur near injection sites, in a human induced activity known as <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3109\">induced seismicity<\/a><\/b><span style=\"font-weight: 400\">. \u00a0<\/span>The significant increase in drilling activity in the central United States has spurred the requirement for the disposal of significant amounts of waste drilling fluid, resulting in a measurable change in the cumulative number of earthquakes experienced in the region.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-62\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-62\" class=\"h5p-iframe\" data-content-id=\"62\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.6 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4313\" aria-describedby=\"caption-attachment-4313\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.6-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-634\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.6-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4313\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.6 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>9.7 Measuring Earthquakes<\/strong><\/h2>\n<h3><b>9.7.1 Seismographs<\/b><\/h3>\n<figure id=\"attachment_3371\" aria-describedby=\"caption-attachment-3371\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.5-seismograph-horiz.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-635 size-medium\" title=\"Source: IRIS https:\/\/www.iris.edu\/hq\/inclass\/animation\/seismograph_horizontal See website for usage rights.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph-horiz-300x225.gif\" alt=\"Animation depicts a seismograph consisting of swinging-gate pendulum with a pencil on the end that shakes back and forth when encountering seismic wave.\" width=\"300\" height=\"225\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph-horiz-300x225.gif 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph-horiz-65x49.gif 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph-horiz-225x169.gif 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph-horiz-350x263.gif 350w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3371\" class=\"wp-caption-text\">Animation of a horizontal seismograph.<\/figcaption><\/figure>\n<p>People feel approximately 1 million earthquakes a year, usually when they are close to the source and the earthquake registers at least <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 2.5. Major earthquakes of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 7.0 and higher are extremely rare. The U. S. Geological Survey (USGS) Earthquakes Hazards Program <a href=\"http:\/\/earthquake.usgs.gov\/earthquakes\/map\/#%7B%22feed%22%3A%227day_all%22%2C%22search%22%3Anull%2C%22listFormat%22%3A%22default%22%2C%22sort%22%3A%22newest%22%2C%22basemap%22%3A%22grayscale%22%2C%22autoUpdate%22%3Atrue%2C%22restrictListToMap%22%3Atrue%2C%22timeZone%22%3A%22utc%22%2C%22mapposition%22%3A%5B%5B32.93492866908233%2C-125.88134765625%5D%2C%5B47.97521412341618%2C-104.32617187499999%5D%5D%2C%22overlays%22%3A%7B%22plates%22%3Atrue%7D%2C%22viewModes%22%3A%7B%22map%22%3Atrue%2C%22list%22%3Atrue%2C%22settings%22%3Atrue%2C%22help%22%3Afalse%7D%7D\">real-time map<\/a> shows the location and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> of recent earthquakes around the world.<\/p>\n<p>To accurately study <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves, geologists use <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a><\/strong> that can measure even the slightest ground vibrations. Early 20<sup>th<\/sup>-century seismograms use a weighted pen (pendulum) suspended by a long <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3174\">spring<\/a> above a recording device fixed solidly to the ground. The recording device is a rotating drum mounted with a continuous strip of paper. During an earthquake, the suspended pen stays motionless and records ground movement on the paper strip. The resulting graph a seismogram. Digital versions use magnets, wire coils, electrical sensors, and digital signals instead of mechanical pens, springs, drums, and paper. A <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismograph<\/a> array is multiple <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> configured to measure vibrations in three directions: north-south (x <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axis<\/a>), east-west (y <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axis<\/a>), and up-down (z <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axis<\/a>).<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3372\" aria-describedby=\"caption-attachment-3372\" style=\"width: 600px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.5-seismograph_vert.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-636 size-full\" title=\"Source: IRIS https:\/\/www.iris.edu\/hq\/inclass\/animation\/seismograph_vertical See website for usage rights.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.5-seismograph_vert.gif\" alt=\"Depicts a vertical seismograph, and earthquake waves traveling past the device. The device consist of a rotating recording drum, where a mass and pencil on a spring bounce vertically when earthquake waves pass trough them.\" width=\"600\" height=\"450\" \/><\/a><figcaption id=\"caption-attachment-3372\" class=\"wp-caption-text\">Animation of how a basic vertical seismograph records seismic waves.<\/figcaption><\/figure>\n<figure id=\"attachment_3374\" aria-describedby=\"caption-attachment-3374\" style=\"width: 1094px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.7-Seismogram.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-637 size-full\" title=\"Made by Paul Inkenbrandt using example data from IRIS.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram.png\" alt=\"Squiggly lines along a horizontal axis. When the P-wave arrives, a small amplitude squiggle shows up. Then the S-wave arrives, and another small-amplitude squiggle shows. Finally, the surface-waves arrive, and large-amplitude waves show up, two to three times the amplitude of the body waves. Then the wave taper off and the line becomes essentially horizontal again.\" width=\"1094\" height=\"398\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram.png 1094w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram-300x109.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram-1024x373.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram-768x279.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram-65x24.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram-225x82.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/09.7-Seismogram-350x127.png 350w\" sizes=\"auto, (max-width: 1094px) 100vw, 1094px\" \/><\/a><figcaption id=\"caption-attachment-3374\" class=\"wp-caption-text\">A seismogram showing the arrivals of the P, S, and surface waves<\/figcaption><\/figure>\n<p>To pinpoint the location of an earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a>, seismologists use the differences in arrival times of the P, S, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a>. After an earthquake, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P waves<\/a> will appear first on a seismogram, followed by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3090\">S waves<\/a>, and finally <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a>, which have the largest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a>. It is important to note that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a> lose energy quickly, so they are not measurable at great distances from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a>. These time differences determine the distance but not the direction of the epicenter. By using wave arrival times recorded on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> at multiple stations, seismologists can apply triangulation to pin point the location of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a> of an earthquake. At least three seismograph stations are needed for triangulation. The distance from each station to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a> is plotted as the radius of a circle. The epicenter is demarked where the circles intersect. This method also works in 3D, using multi-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axis<\/a> seismographs and sphere radii to calculate the underground depth of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a>.<\/p>\n<p style=\"text-align: left\">This video shows the method of triangulation to locate the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a> of an earthquake.<\/p>\n<figure id=\"attachment_4295\" aria-describedby=\"caption-attachment-4295\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-638\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Epicenter-Triangulation-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4295\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-5\" title=\"Earthquake Epicenter Location\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/oBS7BKqHRhs?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><b>9.7.2 Seismograph Network<\/b><\/h3>\n<figure id=\"attachment_3375\" aria-describedby=\"caption-attachment-3375\" style=\"width: 483px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/GSN_topo_20March2017.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-639\" title=\"http:\/\/www.iris.edu\/hq\/programs\/gsn\/maps\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/GSN_topo_20March2017-300x183.jpg\" alt=\"World map of a global network of seismic stations. The map shows that seismic stations are widespread and there are many on every continent.\" width=\"483\" height=\"295\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/GSN_topo_20March2017-300x183.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/GSN_topo_20March2017-65x40.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/GSN_topo_20March2017-225x137.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/GSN_topo_20March2017-350x213.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/GSN_topo_20March2017.jpg 746w\" sizes=\"auto, (max-width: 483px) 100vw, 483px\" \/><\/a><figcaption id=\"caption-attachment-3375\" class=\"wp-caption-text\">Global network of seismic stations. Note that this map does not show all of the world&#8217;s seismic stations, just one of the networks of stations scientists use to measure seismic activity.<\/figcaption><\/figure>\n<p style=\"text-align: left\"><span style=\"font-weight: 400\">The <\/span><a href=\"http:\/\/www.isc.ac.uk\/registries\/\"><span style=\"font-weight: 400\">International Registry of Seismograph Stations<\/span><\/a><span style=\"font-weight: 400\"> lists more than 20,000 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> on the planet.\u00a0<\/span>By comparing data from multiple <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a>, scientists can map the properties of the inside of the Earth, detect detonations of large explosive devices, and predict <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a>. The <a href=\"https:\/\/earthquake.usgs.gov\/monitoring\/gsn\/\">Global Seismic Network<\/a>, a worldwide set of linked <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> that electronically distribute real-time data, includes more than 150 stations that meet specific design and precision standards. The <a href=\"http:\/\/www.usarray.org\/\">USArray<\/a> is a network of hundreds of permanent and transportable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> in the United States that are used to map the subsurface activity of earthquakes (see video).<\/p>\n<p>Along with monitoring for earthquakes and related hazards, the Global <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">Seismograph<\/a> Network helps detect nuclear weapons testing, which is monitored by the <a href=\"https:\/\/www.ctbto.org\/\">Comprehensive Nuclear Test Ban Treaty Organization<\/a>.\u00a0 Most recently, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> have been used to determine nuclear weapons testing by North Korea.<\/p>\n<figure id=\"attachment_4302\" aria-describedby=\"caption-attachment-4302\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Nepal-Earthquake-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-640\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Nepal-Earthquake-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4302\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-6\" title=\"Nepal Earthquake M7.9 Ground Motion Visualization\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/5xc-rNOISQE?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p style=\"text-align: center\"><span style=\"font-size: 10pt\"><em>Nepal Earthquake M7.9 Ground Motion Visualization<\/em><\/span><\/p>\n<h3><b>9.7.3 Seismic tomography<\/b><\/h3>\n<p><span style=\"font-weight: 400\">Very much like a CT (Computed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3096\">Tomography<\/a>) scan uses X-rays at different angles to image the inside of a body, <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3096\">tomography<\/a><\/b><span style=\"font-weight: 400\"> uses <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> rays from thousands of earthquakes that occur each year, <\/span>passing at all angles through masses of rock, to generate images of internal Earth structures.<\/p>\n<figure id=\"attachment_3376\" aria-describedby=\"caption-attachment-3376\" style=\"width: 480px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Speeds_of_seismic_waves.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-641\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-300x205.png\" alt=\"Speed of seismic waves with depth in the earth. Two thousand kilometers is 1240 miles.\" width=\"480\" height=\"327\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-300x205.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-1024x698.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-768x524.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-65x44.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-225x153.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves-350x239.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Speeds_of_seismic_waves.png 1321w\" sizes=\"auto, (max-width: 480px) 100vw, 480px\" \/><\/a><figcaption id=\"caption-attachment-3376\" class=\"wp-caption-text\">Speed of seismic waves with depth in the earth. Two thousand kilometers is 1240 miles.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">Using the assumption that the earth consists of homogenous layers, geologists developed a model of expected properties of earth materials at every depth within the earth called the PREM (Preliminary Reference Earth Model). These properties include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic wave<\/a> transmission velocity, which is dependent on rock density and elasticity. In the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2586\">mantle<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2689\">temperature<\/a> differences affect rock density. Cooler rocks have a higher density and therefore transmit <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves faster. <\/span><span style=\"font-weight: 400\">Warmer rocks have a lower density and transmit earthquake waves slower.\u00a0 When the arrival times of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> rays at individual seismic stations are compared to arrival times predicted by PREM, differences are called\u00a0 <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3097\">seismic anomalies<\/a> <\/b><span style=\"font-weight: 400\">and can be measured for bodies of rock within the earth from\u00a0 seismic rays passing through them at stations of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> network.\u00a0 Because <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> rays travel at all angles from lots of earthquakes and arrive at lots of stations of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> network, like CT scans of the body, variations in the properties of the rock bodies allow 3D images to be constructed of the rock bodies through which the rays passed. Seismologists are thus able to construct 3D images of the interior of the Earth..<\/span><\/p>\n<p><span style=\"font-weight: 400\">For example, seismologists have mapped the Farallon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">Plate<\/a>, a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2576\">tectonic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subducted<\/a> beneath North America during the last several million years, and the Yellowstone <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1185\">magma chamber<\/a>, which is a product of the Yellowstone <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2638\">hot spot<\/a> under the North American <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2575\">continent<\/a>. Peculiarities of the Farallon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">Plate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subduction<\/a> are thought to be responsible for many features of western North America including the Rocky Mountains <\/span><span style=\"font-weight: 400\">(<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/8-earth-history\/\">See chapter 8<\/a>)<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3377\" aria-describedby=\"caption-attachment-3377\" style=\"width: 425px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/New_Plume.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-642\" title=\"From: http:\/\/www.uusatrg.utah.edu\/\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/New_Plume-300x222.jpg\" alt=\"Seismic tomograph showing the magma chamber beneath Yellowstone National Park\" width=\"425\" height=\"315\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/New_Plume-300x222.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/New_Plume-65x48.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/New_Plume-225x167.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/New_Plume-350x259.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/New_Plume.jpg 750w\" sizes=\"auto, (max-width: 425px) 100vw, 425px\" \/><\/a><figcaption id=\"caption-attachment-3377\" class=\"wp-caption-text\">Seismic tomograph showing the magma chamber beneath Yellowstone National Park.<\/figcaption><\/figure>\n<figure id=\"attachment_3378\" aria-describedby=\"caption-attachment-3378\" style=\"width: 358px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Farallon_Plate-e1490562202658.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-643\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Farallon_Plate-e1490562202658-300x276.jpg\" alt=\"Tomographic image of the Farallon plate in the mantle.\" width=\"358\" height=\"330\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Farallon_Plate-e1490562202658-300x276.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Farallon_Plate-e1490562202658-65x60.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Farallon_Plate-e1490562202658-225x207.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Farallon_Plate-e1490562202658-350x322.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Farallon_Plate-e1490562202658.jpg 519w\" sizes=\"auto, (max-width: 358px) 100vw, 358px\" \/><\/a><figcaption id=\"caption-attachment-3378\" class=\"wp-caption-text\">Tomographic image of the Farallon plate in the mantle below North America.<\/figcaption><\/figure>\n<h3><b>9.7.4 Earthquake Magnitude and Intensity<\/b><\/h3>\n<h4><em>9.7.4.1 RICHTER SCALE<\/em><\/h4>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">Magnitude<\/a><\/strong> is the measure of the energy released by an earthquake. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter scale<\/a><\/strong> (M<sub>L<\/sub>), the first and most well-known <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> scale, was developed by Charles F. Richter (1900-1985) at the California Institute of Technology. This was the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> scale used historically by early seismologists. <\/span>Used by early seismologists, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter magnitude<\/a> (M<sub>L<\/sub>) is determined from the maximum <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a> of the pen tracing on the seismogram recording. Adjustments for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a> distance from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismograph<\/a> are made using the arrival-time differences of S and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3086\">P waves<\/a>.<\/p>\n<p><span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter Scale<\/a> is logarithmic, based on powers of 10. This means an increase of one Richter unit represents a 10-fold increase in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a>-wave <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a> or in other words, a\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> 6 earthquake shakes the ground 10 times more than a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> 5. However, the <em>actual energy released<\/em> for each <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> unit is 32 times greater, which means a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> 6 earthquake releases 32 times more energy than a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> 5. <\/span><\/p>\n<p><span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter Scale<\/a> was developed for earthquakes in Southern California, using local <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a>. It has limited applications for larger distances and very large earthquakes. Therefore, most agencies no longer use the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter Scale<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">Moment magnitude<\/a> (M<sub>W<\/sub>), which is measured using <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> arrays and generates values comparable to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter Scale<\/a>, is more accurate for measuring earthquakes across the Earth, including large earthquakes, although they require more time to calculate. News media often report Richter magnitudes right after an earthquake occurs even though scientific calculations now use moment magnitudes.<\/span><\/p>\n<h4><em><b>9.7.4.2 MOMENT MAGNITUDE SCALE<\/b><\/em><\/h4>\n<p><span style=\"font-weight: 400\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">Moment Magnitude<\/a> scale<\/strong> depicts the absolute size of earthquakes, comparing information from multiple locations and using a measurement of actual energy released calculated from cross-sectional area of rupture, amount of slippage, and the rigidity of the rocks. Because each earthquake occurs in a unique geologic setting and the rupture area is often hard to measure, estimates of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> can take days or even months to calculate. <\/span><\/p>\n<p><span style=\"font-weight: 400\">Like the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter Scale<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> scale is logarithmic. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">Magnitude<\/a> values of the two scales are approximately equal, except for very large earthquakes. Both scales are used for reporting earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter Scale<\/a> provides a quick <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> estimate immediately following the quake and thus, is usually reported in news accounts. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">Moment magnitude<\/a> calculations take much longer but are more accurate and thus, more useful for scientific analysis. <\/span><\/p>\n<figure id=\"attachment_4301\" aria-describedby=\"caption-attachment-4301\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Moment-Magnitude-Explained-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-644\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Moment-Magnitude-Explained-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4301\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-7\" title=\"Moment Magnitude Explained\u2014What Happened to the Richter Scale?\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/HL3KGK5eqaw?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h4><em><b>9.7.4.3 Modified Mercalli Intensity Scale<\/b><\/em><\/h4>\n<p><span style=\"font-weight: 400\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3101\">Modified Mercalli Intensity Scale<\/a> (MMI) <\/strong><\/span>is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2647\">qualitative<\/a> rating of ground-shaking intensity based on observable structural damage and people\u2019s perceptions. This scale uses a <span style=\"font-style: normal !msorm\"><em>I<\/em><\/span> (Roman numeral one) rating for the lowest intensity and <span style=\"font-style: normal !msorm\"><em>X<\/em><\/span> (ten) for the highest (see table) and can vary depending on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a> location and population density, such as urban versus rural settings. Historically, scientists used the MMI Scale to categorize earthquakes before they developed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2646\">quantitative<\/a> measurements of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a>. Intensity maps show locations of the most severe damage, based on residential questionnaires, local news articles, and on-site assessment reports.<\/p>\n<table style=\"width: 111.56%;height: 868px\">\n<thead>\n<tr style=\"height: 28px\">\n<th style=\"width: 11.7105%;text-align: center;height: 28px\">Intensity<\/th>\n<th style=\"width: 13.8101%;text-align: center;height: 28px\">Shaking<\/th>\n<th style=\"width: 74.3478%;height: 28px\">Description\/Damage<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr style=\"height: 28px\">\n<td style=\"background-color: #ffffff;width: 11.7105%;text-align: center;vertical-align: middle;height: 28px\">I<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 28px\">Not felt<\/td>\n<td style=\"width: 74.3478%;height: 28px\">Not felt except by a very few under especially favorable conditions.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #dfe6fe;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">II<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Weak<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Felt only by a few persons at rest,especially on upper floors of buildings.<\/td>\n<\/tr>\n<tr style=\"height: 140px\">\n<td style=\"background-color: #82f9fb;width: 11.7105%;text-align: center;vertical-align: middle;height: 140px\">III<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 140px\">Weak<\/td>\n<td style=\"width: 74.3478%;height: 140px\">Felt quite noticeably by persons indoors, especially on upper floors of buildings.<br \/>\nMany people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.<\/td>\n<\/tr>\n<tr style=\"height: 140px\">\n<td style=\"background-color: #7efbdf;width: 11.7105%;text-align: center;vertical-align: middle;height: 140px\">IV<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 140px\">Light<\/td>\n<td style=\"width: 74.3478%;height: 140px\">Felt indoors by many, outdoors by few during the day. At night, some awakened.<br \/>\nDishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #95f879;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">V<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Moderate<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #f7f835;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">VI<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Strong<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.<\/td>\n<\/tr>\n<tr style=\"height: 112px\">\n<td style=\"background-color: #fdca2c;width: 11.7105%;text-align: center;vertical-align: middle;height: 112px\">VII<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 112px\">Very strong<\/td>\n<td style=\"width: 74.3478%;height: 112px\">Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.<\/td>\n<\/tr>\n<tr style=\"height: 112px\">\n<td style=\"background-color: #ff701f;width: 11.7105%;text-align: center;vertical-align: middle;height: 112px\">VIII<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 112px\">Severe<\/td>\n<td style=\"width: 74.3478%;height: 112px\">Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.<\/td>\n<\/tr>\n<tr style=\"height: 84px\">\n<td style=\"background-color: #ec2516;width: 11.7105%;text-align: center;vertical-align: middle;height: 84px\">IX<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 84px\">Violent<\/td>\n<td style=\"width: 74.3478%;height: 84px\">Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.<\/td>\n<\/tr>\n<tr style=\"height: 56px\">\n<td style=\"background-color: #c81e11;width: 11.7105%;text-align: center;vertical-align: middle;height: 56px\">X<\/td>\n<td style=\"width: 13.8101%;text-align: center;vertical-align: middle;height: 56px\">Extreme<\/td>\n<td style=\"width: 74.3478%;height: 56px\">Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><a href=\"https:\/\/earthquake.usgs.gov\/learn\/topics\/mercalli.php\"><i><span style=\"font-weight: 400\">Table. Abridged Mercalli Scale from USGS General Interest Publication 1989-288-913.<\/span><\/i><\/a><\/p>\n<h4><em><b>9.7.4.4 Shake Maps<\/b><\/em><\/h4>\n<figure id=\"attachment_3379\" aria-describedby=\"caption-attachment-3379\" style=\"width: 408px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/shakemapintensity-e1490409875228.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-645\" title=\"https:\/\/earthquake.usgs.gov\/earthquakes\/eventpage\/nc17204#shakemap\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/shakemapintensity-e1490409875228-273x300.jpg\" alt=\"Example of a shake map.\" width=\"408\" height=\"449\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/shakemapintensity-e1490409875228-273x300.jpg 273w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/shakemapintensity-e1490409875228-65x72.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/shakemapintensity-e1490409875228-225x248.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/shakemapintensity-e1490409875228-350x385.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/shakemapintensity-e1490409875228.jpg 549w\" sizes=\"auto, (max-width: 408px) 100vw, 408px\" \/><\/a><figcaption id=\"caption-attachment-3379\" class=\"wp-caption-text\">Example of a shake map.<\/figcaption><\/figure>\n<p>Shake maps, written ShakeMaps by the USGS, use high-quality, computer-interpolated data from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismograph<\/a>\u00a0networks to show areas of intense shaking. Shake maps are useful in the crucial minutes after an earthquake, as they show emergency personnel where the greatest damage likely occurred and help them locate possibly damaged gas lines and other utility facilities.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-63\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-63\" class=\"h5p-iframe\" data-content-id=\"63\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.7 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4247\" aria-describedby=\"caption-attachment-4247\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-588\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4247\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.7 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>9.8 Earthquake Risk<\/strong><\/h2>\n<h3><b>9.8.1<\/b>\u00a0 \u00a0Factors that Determine Shaking<\/h3>\n<p>Earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> is an absolute value that measures pure energy release. Intensity however, i.e. how much the ground shakes, is a determined by several factors.<b><\/b><b><\/b><\/p>\n<p><strong>Earthquake <\/strong><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">Magnitude<\/a><\/strong><strong>\u2014<\/strong>In general, the larger the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a>, the stronger the shaking and the longer the shaking will last.<\/p>\n<p><span style=\"font-weight: 400\">This table is taken from from the <a href=\"https:\/\/earthquake.usgs.gov\/learn\/topics\/mag_vs_int.php\">USGS<\/a> and shows scales of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3101\">Mercalli<\/a> Intensity, and descriptions of shaking and resulting damage.<\/span><\/p>\n<table style=\"width: 762px\">\n<tbody>\n<tr>\n<td style=\"width: 88px\"><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">Magnitude<\/a><\/b><\/td>\n<td style=\"text-align: center;width: 103px\"><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3101\">Modified Mercalli Intensity<\/a><\/b><\/td>\n<td style=\"width: 528px\"><b>Shaking\/Damage Description<\/b><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>1.0 &#8211; 3.0<\/b><\/td>\n<td style=\"width: 103px;background-color: #69fad3;text-align: center;vertical-align: middle\"><b>I<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Only felt by a very few. <\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>3.0 &#8211; 3.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #82f056;text-align: center;vertical-align: middle\"><b>II &#8211; III<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Noticeable indoors, especially on upper floors.<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>4.0 &#8211; 4.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #eaf03c;text-align: center;vertical-align: middle\"><b>IV &#8211; V<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Most to all feel it. Dishes, doors, cars shake and possibly break.<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>5.0 &#8211; 5.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #edac3b;text-align: center;vertical-align: middle\"><b>VI &#8211; VII<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Everyone feels it. Some items knocked over or broken. Building damage possible.<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>6.0 &#8211; 6.9<\/b><\/td>\n<td style=\"width: 103px;background-color: #eb5c15;text-align: center;vertical-align: middle\"><b>VII &#8211; IX<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Frightening amounts of shaking. Significant damage especially with poorly constructed buildings<\/span><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;width: 88px;vertical-align: middle\"><b>\u2265 7.0<\/b><\/td>\n<td style=\"width: 103px;background-color: #f70202;text-align: center;vertical-align: middle\"><b>\u2265 VIII<\/b><\/td>\n<td style=\"width: 528px;vertical-align: middle\"><span style=\"font-weight: 400\">Significant destruction of buildings. Potential for objects to be thrown in air from shaking.<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h4><span style=\"font-weight: 400\">\u00a0<\/span><\/h4>\n<p><strong>Location and Direction\u2014<\/strong>Shaking is more severe closer to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a>. The severity of shaking is influenced by the location of the observer relative to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3085\">epicenter<\/a>, direction of rupture propagation, and path of greatest rupture.<\/p>\n<p><strong>Local Geologic Conditions<\/strong><strong>\u2014<\/strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">Seismic<\/a> waves are affected by the nature of the ground materials through which they pass. Different materials respond differently to an earthquake. Think of shaking a block of Jello versus a meatloaf, one will jiggle much more when hit by waves of the same <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a>. The ground\u2019s response to shaking depends on the degree of substrate consolidation. Solid sedimentary, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2675\">igneous<\/a>, or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2914\">metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1971\">bedrock<\/a> shakes less than unconsolidated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediments<\/a>.<\/p>\n<p>This video shows how different substrates behave in response to different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves and their potential for destruction.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_4293\" aria-describedby=\"caption-attachment-4293\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Amplification-and-Liquefaction-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-646 size-thumbnail\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Amplification-and-Liquefaction-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4293\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-8\" title=\"Amplification and Liquefaction Animation (Educational)\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/536xSZ_XkSs?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">Seismic<\/a> waves move fastest through consolidated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1971\">bedrock<\/a>, slower through unconsolidated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediments<\/a>, and slowest through unconsolidated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediments<\/a> with a high water content. Seismic energy is transmitted by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3187\">wave velocity<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a>. When seismic waves slow down, energy is transferred to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a>, increasing the motion of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a>, which in turn amplifies ground shaking.<\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">Focus<\/a> depth<i style=\"font-size: 16px;font-weight: 400\">\u2014<\/i><\/strong>Deeper earthquakes cause less surface shaking because much of their energy, transmitted as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3088\">body waves<\/a>, is lost before reaching the surface. Recall that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a> are generated by P and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3090\">S waves<\/a> impacting the Earth\u2019s surface.<\/p>\n<h3><b>9.8.2<\/b>\u00a0 \u00a0Factors that Determine Destruction<\/h3>\n<p>Just as certain conditions will impact intensity of ground-shaking, several factors affect how much destruction is caused.<\/p>\n<figure id=\"attachment_3380\" aria-describedby=\"caption-attachment-3380\" style=\"width: 347px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-647\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake-300x199.jpg\" alt=\"Example of devastation on unreinforced masonry by seismic motion.\" width=\"347\" height=\"230\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake-300x199.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake-65x43.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake-225x149.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake-350x232.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Collapse_of_Unreinforced_Masonry_Buildings_Iran_Persia_-_1990_Manjil_Roudbar_Earthquake.jpg 751w\" sizes=\"auto, (max-width: 347px) 100vw, 347px\" \/><\/a><figcaption id=\"caption-attachment-3380\" class=\"wp-caption-text\">Example of devastation on unreinforced masonry by seismic motion.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><strong>Building Materials\u2014<\/strong><span style=\"font-weight: 400\">The flexibility of a building material determines its resistance to earthquake damage. Unreinforced masonry (URM) is the material most devastated by ground shaking. Wood framing fastened with nails bends and flexes during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic wave<\/a> passage and is more likely to survive intact. Steel also has the ability to deform elastically before <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2583\">brittle<\/a> failure. The <a href=\"http:\/\/www.bereadyslc.com\/fix-the-bricks\/\">Fix the Bricks<\/a> campaign in Salt Lake City, Utah <\/span><span style=\"font-weight: 400\">has good information on URMs and earthquake safety.\u00a0<\/span><\/p>\n<p><i><\/i><strong>Intensity <\/strong><strong>a<\/strong><strong>nd Duration<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">Greater shaking and duration of shaking causes more destruction than lower and shorter shaking.<\/span><\/p>\n<p style=\"text-align: left\"><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3103\">Resonance<\/a><strong>\u2014<\/strong><\/b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3103\">Resonance <\/a>occurs when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic wave<\/a> frequency matches a building\u2019s natural shaking frequency and increases the shaking happened in the 1985 Mexico City Earthquake, where buildings of heights between 6 and 15 stories were especially vulnerable to earthquake damage. Skyscrapers designed with earthquake resilience have dampers and base isolation features to reduce <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3103\">resonance<\/a>.<\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3103\">Resonance<\/a> is influenced by the properties of the building materials. Changes in the structural integrity of a building can alter <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3103\">resonance<\/a><span style=\"font-weight: 400\">. <\/span>Conversely, changes in measured <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3103\">resonance<\/a> can indicate a potentially altered structural integrity.<\/p>\n<p>These two videos discuss why buildings fall during earthquakes and a modern procedure to reduce potential earthquake destruction for larger buildings.<\/p>\n<figure id=\"attachment_4305\" aria-describedby=\"caption-attachment-4305\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Why-do-buildings-fall-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-648\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Why-do-buildings-fall-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4305\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-9\" title=\"Why do buildings fall in earthquakes? - Vicki V. May\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/H4VQul_SmCg?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<figure id=\"attachment_4304\" aria-describedby=\"caption-attachment-4304\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Utah-State-Capital-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-649\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Utah-State-Capital-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4304\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-10\" title=\"Utah State Capital Building - Base Isolators\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/DP7fB1I7UwE?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><b>9.8.3 Earthquake Recurrence<\/b><\/h3>\n<figure id=\"attachment_3382\" aria-describedby=\"caption-attachment-3382\" style=\"width: 200px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fault_Trench_RS18376__MG_6182-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3382 size-medium\" title=\"Taken by: Adam Hiscock, Utah Geological Survey 7\/2\/2014\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fault_Trench_RS18376__MG_6182-scaled-1.jpg\" alt=\"Fault trench near Draper Utah. Trenches allow geologists to see a cross section of a fault and to use dating techniques to determine how frequently earthquakes occur.\" width=\"200\" height=\"300\" \/><\/a><figcaption id=\"caption-attachment-3382\" class=\"wp-caption-text\">Fault trench near Draper Utah. Trenches allow geologists to see a cross section of a fault and to use dating techniques to determine how frequently earthquakes occur.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">A long hiatus in activity on along a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> segment with a history of recurring earthquakes is known as a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> gap<\/strong>. The lack of activity may indicate the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> segment is locked, which may produce a buildup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a>\u00a0and higher probability of an earthquake recurring. Geologists dig earthquake trenches across <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> to estimate the frequency of past earthquake occurrences. Trenches are effective for faults with relatively long <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3104\">recurrence<\/a> intervals<\/b>, roughly <span style=\"font-weight: 400\">100s to 10,000s of years\u00a0 between significant earthquakes. Trenches are less useful in areas with more frequent earthquakes because they usually have more recorded data. <\/span><\/p>\n<p>&nbsp;<\/p>\n<h3><b>9.8.4 Earthquake Distribution<\/b><\/h3>\n<p>This video shows the distribution of significant earthquakes on the Earth during the years 2010 through 2012. Like <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1181\">volcanoes<\/a>, earthquakes tend to aggregate around active boundaries of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2576\">tectonic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plates<\/a>. The exception is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">intraplate<\/a> earthquakes, which are comparatively rare..<\/p>\n<figure id=\"attachment_4306\" aria-describedby=\"caption-attachment-4306\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/World-Earthquakes-2010-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-651\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/World-Earthquakes-2010-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4306\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p>https:\/\/youtube.com\/watch?v=Wc6vtj4yYcY<\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">Subduction<\/a> Zones<\/strong><strong>\u2014<\/strong><b><i><\/i><\/b><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">Subduction<\/a> zones, found at <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2600\">convergent<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries, are where the largest and deepest earthquakes, called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3075\">megathrust<\/a> earthquakes, occur. Examples of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subduction<\/a>-zone earthquake areas include the Sumatran Islands, Aleutian Islands, west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2890\">coast<\/a> of South America, and Cascadia <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">Subduction<\/a> Zone off the coast of Washington and Oregon. <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">\u00a0Chapter 2<\/a><a href=\"http:\/\/opengeology.org\/textbook\/2-plate-tectonics\/#231_Subduction\">\u00a0<\/a> for more information about <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subduction<\/a> zones.<\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2620\">Collision<\/a> Zone<\/strong><strong>s<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">Collisions between converging <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2575\">continental<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plates<\/a> create broad earthquake zones that may generate deep, large earthquakes from the remnants of past <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subduction<\/a> events or other deep-crustal processes. The Himalayan Mountains (northern border of the Indian subcontinent) and Alps (southern Europe and Asia) are active regions of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2620\">collision<\/a>-zone earthquakes. <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a> for more information about <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2620\">collision<\/a> zones.<\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">Transform<\/a> <\/strong><strong>Boundaries<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">Strike-slip<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> created at <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a> boundaries produce moderate-to-large earthquakes, usually having a maximum <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> of about 8.\u00a0 The San Andreas <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> (California) is an example of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a>-boundary earthquake zone. Haiti&#8217;s Enriquillo-Plantain Garden <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2664\">system<\/a>, which caused the 2010 earthquake near Port-au-Prince (see below), and Septentrional <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a>, which destroyed Cap-Ha\u00eftien in 1842 and shook Cuba in 2020, are also <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a>. Other examples are the Alpine <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a> (New Zealand) and Anatolian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Faults<\/a> (Turkey). <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a> for more information about <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a> boundaries.<\/p>\n<p style=\"text-align: left\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2599\">Divergent<\/a> Boundaries<\/strong><b>\u2014<\/b><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2575\">Continental<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2624\">rifts<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2630\">mid-ocean ridges<\/a> found at <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2599\">divergent<\/a> boundaries generally produce moderate earthquakes. Examples of active earthquake zones include the East African <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2624\">Rift<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2664\">System<\/a> (southwestern Asia through eastern Africa), Iceland, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a> province (Nevada, Utah, California, Arizona, and northwestern Mexico). <\/span>See <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a> for more information about <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2599\">divergent<\/a> boundaries.<\/p>\n<figure id=\"attachment_3383\" aria-describedby=\"caption-attachment-3383\" style=\"width: 354px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-652\" title=\"By Kbh3rd (Own work) [CC BY-SA 3.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_.png\" alt=\"Map showing concentration of earthquakes near the border of Missouri, Kentucky, Tennessee, and Illinois\" width=\"354\" height=\"373\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_.png 569w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_-285x300.png 285w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_-65x69.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_-225x237.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/569px-New_Madrid_Seismic_Zone_activity_1974-2011.svg_-350x369.png 350w\" sizes=\"auto, (max-width: 354px) 100vw, 354px\" \/><\/a><figcaption id=\"caption-attachment-3383\" class=\"wp-caption-text\">High density of earthquakes in the New Madrid seismic zone.<\/figcaption><\/figure>\n<p style=\"text-align: left\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">Intraplate<\/a> Earthquakes<\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">Intraplate<\/a> earthquakes are not found near <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2576\">tectonic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries, but generally occur in areas of weakened <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3333\">concentrated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2918\">tectonic stress<\/a>. The New Madrid <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> zone, which covers Missouri, Illinois, Tennessee, Arkansas, and Indiana, is thought to represent the failed Reelfoot <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2624\">rift<\/a><\/span><span style=\"font-weight: 400\">. <\/span>The failed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2624\">rift<\/a> zone weakened the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a>, making it more responsive to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2576\">tectonic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> movement and interaction. Geologists theorize the infrequently occurring earthquakes are produced by low <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">strain<\/a> rates<\/p>\n<h3><b>9.8.5 Secondary Hazards Caused by Earthquakes<\/b><\/h3>\n<p style=\"text-align: left\">Most earthquake damage is caused by ground shaking and fault block displacement\u00a0 In addition, there are secondary hazards that endanger structures and people, in some cases after the shaking stops.<\/p>\n<figure id=\"attachment_2478\" aria-describedby=\"caption-attachment-2478\" style=\"width: 500px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Liquefaction_at_Niigata-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-44 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction_at_Niigata-1.jpg\" alt=\"Buildings toppled from liquefaction during a 7.5 magnitude earthquake in Japan.\" width=\"500\" height=\"297\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction_at_Niigata-1.jpg 500w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction_at_Niigata-1-300x178.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction_at_Niigata-1-65x39.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction_at_Niigata-1-225x134.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction_at_Niigata-1-350x208.jpg 350w\" sizes=\"auto, (max-width: 500px) 100vw, 500px\" \/><\/a><figcaption id=\"caption-attachment-2478\" class=\"wp-caption-text\">Buildings toppled from liquefaction during a 7.5 magnitude earthquake in Japan.<\/figcaption><\/figure>\n<p>Buildings toppled from liquefaction during a 7.5 magnitude earthquake in Japan.<\/p>\n<p style=\"text-align: left\"><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3106\">Liquefaction<\/a>\u2014<\/strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3106\">Liquefaction<\/a> occurs when water-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2706\">saturated<\/a>, unconsolidated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediments<\/a>, usually silt or sand, become fluid-like from shaking. The shaking breaks the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2692\">cohesion<\/a> between grains of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediment<\/a>, creating a slurry of particles suspended in water. Buildings settle or tilt in the liquified <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediment<\/a>, which looks very much like quicksand in the movies. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3106\">Liquefaction<\/a> also creates sand <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1181\">volcanoes<\/a>, cone-shaped features created when liquefied sand is squirted through an overlying and usually finer-grained layer.<\/span><\/p>\n<p>This video demonstrates how <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3106\">liquefaction<\/a> takes place.<\/p>\n<figure id=\"attachment_4299\" aria-describedby=\"caption-attachment-4299\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Liquefaction-Demonstrated-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-653\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Liquefaction-Demonstrated-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4299\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-11\" title=\"Liquefaction Demonstrated\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/b_aIm5oi5eA?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p>This video shows <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3106\">liquefaction<\/a> occurring during the 2011 earthquake in Japan.<\/p>\n<figure id=\"attachment_4298\" aria-describedby=\"caption-attachment-4298\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-654\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Great-Eastern-Japan-Earthquake-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4298\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-12\" title=\"Great Eastern Japan Earthquake - Liquefaction in Makuhari\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/rn3oAvmZY8k?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">Tsunamis<\/a><\/strong><strong>\u2014<\/strong><span style=\"font-weight: 400\">Among the most devastating natural disasters are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a>, earthquake-induced ocean waves. When the sea floor is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3081\">offset<\/a> by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> movement or an underwater <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1199\">landslide<\/a>, the ground displacement lifts a volume of ocean water and generates the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunami<\/a> wave. Ocean wave behavior, which includes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a>, is covered in <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/12-shorelines\/\">Chapter 12<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">Tsunami<\/a> waves are fast-moving with low <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a> in deep ocean water but grow significantly in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3184\">amplitude<\/a> in the shallower waters approaching <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3195\">shore<\/a>. <\/span>When a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunami<\/a> is about to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> land, the drawback of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3183\">trough<\/a> preceding the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3182\">wave crest<\/a> causes the water to recede dramatically from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3195\">shore<\/a>. Tragically, curious people wander out and follow the disappearing water, only to be overcome by an oncoming wall of water that can be upwards of a 30 m (100 ft) high. Early warning systems help mitigate the loss of life caused by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a>.<\/p>\n<figure id=\"attachment_3385\" aria-describedby=\"caption-attachment-3385\" style=\"width: 429px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/09.8_Propagation_tsunami.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-655 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/09.8_Propagation_tsunami.gif\" alt=\"Animated gif showing large wavelength, low-amplitude waves in the deep ocean and high-amplitude, low-wavelength waves in the shallow ocean. Frequency decreases with depth.\" width=\"429\" height=\"225\" \/><\/a><figcaption id=\"caption-attachment-3385\" class=\"wp-caption-text\">As the ocean depth becomes shallower, the wave slows down and pile up on top of itself, making large, high-amplitude waves.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3387\" aria-describedby=\"caption-attachment-3387\" style=\"width: 431px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/RS13929_S2120-scr.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-656\" title=\"https:\/\/geodata.geology.utah.gov\/pages\/view.php?ref=13929&amp;amp;k=&amp;amp;search=springdale&amp;amp;offset=144&amp;amp;order_by=date&amp;amp;sort=DESC&amp;amp;archive=0\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-300x212.jpg\" alt=\"Broken house offset and destroyed from a landslide.\" width=\"431\" height=\"305\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-300x212.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-1024x724.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-768x543.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-65x46.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-225x159.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr-350x248.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/RS13929_S2120-scr.jpg 1100w\" sizes=\"auto, (max-width: 431px) 100vw, 431px\" \/><\/a><figcaption id=\"caption-attachment-3387\" class=\"wp-caption-text\">House in Springdale, Utah destroyed by earthquake-triggered landslide.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1199\">Landslides<\/a>\u2014<\/strong><\/span>Shaking can <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3117\">trigger<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1199\">landslides<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/10-mass-wasting\/\">Chapter 10<\/a>). In 1992 a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 5.9 earthquake in St. George, Utah, caused a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1199\">landslide<\/a> that destroyed several structures in the Balanced Rock Hills subdivision in Springville, Utah<span style=\"font-weight: 400\">.\u00a0\u00a0<\/span><\/p>\n<p><strong>Seiches<\/strong><strong>\u2014S<\/strong>eiches are waves generated in lakes by earthquakes. The shaking may cause water to slosh back-and-forth or sometimes change the lake depth. Seiches in Hebgen Lake during a 1959 earthquake caused major destruction to nearby structures and roads.<\/p>\n<p>This video shows a seich generated in a swimming pool by an earthquake in Nepal in 2015.<\/p>\n<figure id=\"attachment_4296\" aria-describedby=\"caption-attachment-4296\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Earthquake-Nepal-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-657\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earthquake-Nepal-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4296\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><a href=\"https:\/\/youtu.be\/27GMnYEWL0M\">https:\/\/youtu.be\/27GMnYEWL0M<\/a><\/p>\n<p>&nbsp;<\/p>\n<h4><\/h4>\n<p><strong>Land Elevation Changes<\/strong><strong>\u2014<\/strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3079\">Elastic rebound<\/a> and displacement along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> plane can cause significant land elevation changes, such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1464\">subsidence<\/a> or upheaval. The 1964 Alaska earthquake produced significant land elevation changes, with the differences in height between the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3067\">hanging wall<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3068\">footwall<\/a> ranging from one to several meters (3\u201330 ft). The Wasatch Mountains in Utah represent an accumulation of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3107\">fault scarps<\/a> created a few meters at a time, over a few million years.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-64\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-64\" class=\"h5p-iframe\" data-content-id=\"64\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.8 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4315\" aria-describedby=\"caption-attachment-4315\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.8-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-658\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.8-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4315\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.8 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>9.9 Case Studies<\/strong><\/h2>\n<p>Video explaining the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> activity and hazards of the Intermountain <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">Seismic<\/a> Belt and the Wasatch <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a>, a large <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">intraplate<\/a> area of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> activity.<\/p>\n<figure id=\"attachment_4323\" aria-describedby=\"caption-attachment-4323\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Wasatch-Fault-Fly-By-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-659\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Wasatch-Fault-Fly-By-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4323\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-13\" title=\"Wasatch Fault Fly By Video (high quality)\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/DByPiCkznE0?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><b>9.9.1 North American Earthquakes<\/b><\/h3>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a> Earthquakes\u2014<\/strong>Earthquakes in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a> Province, <\/span>from the Wasatch <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a> (Utah) to the Sierra Nevada (California), occur primarily in normal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> created by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">tensional<\/a> forces. The Wasatch <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a>, which defines the eastern extent of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2462\">Basin and Range<\/a> province, has been studied as an earthquake hazard for more than 100 years.<\/p>\n<p><b>New Madrid Earthquakes (1811-1812)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b><span style=\"font-weight: 400\">Historical accounts of earthquakes in the New Madrid <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> zone date as far back as 1699 and earthquakes continue to be reported in modern times<\/span><span style=\"font-weight: 400\">. A sequence of large (M<sub>w<\/sub> &gt;7) occurred from December 1811 to February 1812 in the New Madrid area of Missouri<\/span><span style=\"font-weight: 400\">. The earthquakes damaged houses in St. Louis, affected the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3134\">stream<\/a> course of the Mississippi <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3134\">River<\/a>, and leveled the town of New Madrid. \u00a0These earthquakes were the result of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">intraplate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> activity<\/span><span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<p><b>Charleston (1886)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b><span style=\"font-weight: 400\">The 1886 earthquake in Charleston South Carolina was a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 7.0, with a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3101\">Mercalli<\/a> intensity of X, caused significant ground motion, and killed at least 60 people. \u00a0This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">intraplate<\/a> earthquake was likely associated with ancient <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">faults<\/a> created during the breakup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3366\">Pangea<\/a>. \u00a0The earthquake caused significant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3106\">liquefaction<\/a><\/span><span style=\"font-weight: 400\">. Scientists estimate the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3104\">recurrence<\/a> of destructive earthquakes in this area with an interval of approximately 1500 to 1800 years.<\/span><\/p>\n<p><b>Great San Francisco Earthquake and Fire (1906)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><span style=\"font-weight: 400\">On April 18, 1906, a large earthquake, with an estimated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> of 7.8 and MMI of X, occurred along the San Andreas <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> near San Francisco California. There were multiple <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3084\">aftershocks<\/a> followed by devastating fires, resulting in about 80% of the city being destroyed. Geologists G.K. Gilbert and Richard L. Humphrey, working <\/span><\/b>independently, arrived the day following the earthquake and took measurements and photographs<b><span style=\"font-weight: 400\">.\u00a0<\/span><\/b><\/p>\n<figure id=\"attachment_3388\" aria-describedby=\"caption-attachment-3388\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/1200px-San_Francisco_1906_earthquake_Panoramic_View.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-large wp-image-660\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-1024x129.jpg\" alt=\"Wide view of rubble and skeletons of buildings that remain, some still smoking.\" width=\"1024\" height=\"129\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-1024x129.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-300x38.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-768x97.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-65x8.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-225x28.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View-350x44.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1200px-San_Francisco_1906_earthquake_Panoramic_View.jpg 1200w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-3388\" class=\"wp-caption-text\">Remains of San Francisco after the 1906 earthquake and fire.<\/figcaption><\/figure>\n<p style=\"text-align: left\"><b>Alaska (1964)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b>The 1964 Alaska earthquake, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 9.2, was one of the most powerful earthquakes ever recorded. The earthquake originated in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3075\">megathrust<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> along the Aleutian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subduction<\/a> zone. The earthquake caused large areas of land <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1464\">subsidence<\/a> and uplift, as well as significant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3110\">mass wasting<\/a>.<\/p>\n<p>Video from the USGS about the 1964 Alaska earthquake.<\/p>\n<figure id=\"attachment_4291\" aria-describedby=\"caption-attachment-4291\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/1964-Quake-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-661\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1964-Quake-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4291\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-14\" title=\"1964 Quake: The Great Alaska Earthquake\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/lE2j10xyOgI?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><b>Loma Prieta (1989)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b>The Loma Prieta, California, earthquake was created by movement along the San Andreas <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Fault<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 6.9 earthquake was followed by a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> 5.2 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3084\">aftershock<\/a>. It caused 63 deaths, buckled portions of the several freeways, and collapsed part of the San Francisco-Oakland Bay Bridge.<\/p>\n<p>This video shows how shaking propagated across the Bay Area during the 1989 Loma Prieta earthquake.<\/p>\n<figure id=\"attachment_4317\" aria-describedby=\"caption-attachment-4317\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.9-Video-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-662\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Video-QR-Code.png 1148w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4317\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this interactive activity via this QR Code.<\/figcaption><\/figure>\n<div style=\"width: 300px;\" class=\"wp-video\"><video class=\"wp-video-shortcode\" id=\"video-667-2\" width=\"300\" height=\"200\" preload=\"metadata\" controls=\"controls\"><source type=\"video\/webm\" src=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Lp1989plan_hires.webm?_=2\" \/><a href=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Lp1989plan_hires.webm\">http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Lp1989plan_hires.webm<\/a><\/video><\/div>\n<p><span style=\"font-weight: 400\">This video shows destruction caused by the 1989 Loma Prieta earthquake.<\/span><\/p>\n<figure id=\"attachment_4300\" aria-describedby=\"caption-attachment-4300\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Loma-Prieta-Earthquake-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-663\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Loma-Prieta-Earthquake-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4300\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-15\" title=\"Loma Prieta Earthquake, CA, 1989, Part 1\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/L6jYgqLyIPw?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><b>9.9.2 Global Earthquakes<\/b><\/h3>\n<p>Many of history\u2019s largest earthquakes occurred in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3075\">megathrust<\/a> zones, such as the Cascadia <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">Subduction<\/a> Zone (Washington and Oregon coasts) and Mt. Rainier (Washington).<\/p>\n<p><b>Shaanxi, China (1556)<span style=\"font-weight: 400\"><strong>\u2014<\/strong><\/span><\/b><span style=\"font-weight: 400\">On January 23, 1556 an earthquake of an approximate <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 8 hit central China, killing approximately 830,000 people in what is considered the most deadly earthquake in history.\u00a0<\/span><b><span style=\"font-weight: 400\">The high death toll was attributed to the collapse of cave dwellings (<span style=\"font-style: normal !msorm\"><em>yaodong<\/em><\/span>) built in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2909\">loess<\/a> deposits, which are large banks of windblown, compacted <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2678\">sediment<\/a> (see<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">\u00a0Chapter 5<\/a>). <\/span><\/b>Earthquakes in this are region are believed to have a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3104\">recurrence<\/a> interval of 1000 years.<\/p>\n<p><strong>Lisbon, Portugal (1755)<b><span style=\"font-weight: 400\">\u2014On November 1, 1755 an earthquake with an estimated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> range of 8\u20139 struck Lisbon, Portugal<\/span><\/b><\/strong><span style=\"font-weight: 400\">, killing between 10,000 to 17,400 people<\/span><span style=\"font-weight: 400\">. The earthquake was followed by a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunami<\/a>, which brought the total death toll to between 30,000-70,000 people.<\/span><\/p>\n<p><strong>Valdivia, Chile (1960)<b><span style=\"font-weight: 400\">\u2014The May 22, 1960 earthquake was the most powerful earthquake ever measured, with a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 9.4\u20139.6 and lasting an estimated 10 minutes. <\/span><\/b><\/strong>It triggered <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a> that destroyed houses across the Pacific Ocean in Japan and Hawaii and caused vents to erupt on the Puyehue-Cord\u00f3n Caulle (Chile).<\/p>\n<p>Video describing the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunami<\/a> produced by the 1960 Chili earthquake.<\/p>\n<figure id=\"attachment_4318\" aria-describedby=\"caption-attachment-4318\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Tsunami-Animation-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-664\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Tsunami-Animation-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4318\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-16\" title=\"Tsunami Animation: Valdivia, Chile, 1960 (rotating globe)\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/RHYbprZAIWo?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><b>Tangshan, China (1976)<strong><span style=\"font-weight: 400\">\u2014<\/span><\/strong><\/b>Just before 4 a.m. (Beijing time) on July 28, 1976 a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 7.8 earthquake struck Tangshan (Hebei Province), China, and killed more than 240,000 people. The high death-toll is attributed to people still being asleep or at home and most buildings being made of unreinforced masonry.<\/p>\n<p><strong>Sumatra, Indonesia (2004)<b><span style=\"font-weight: 400\">\u2014On December 26, 2004, slippage of the Sunda <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3075\">megathrust<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> generated a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 9.0\u20139.3 earthquake off the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2890\">coast<\/a> of Sumatra, Indonesia<\/span><\/b><\/strong><span style=\"font-weight: 400\">. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3075\">megathrust<\/a> fault is created by the Australia <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subducting<\/a> below the Sunda plate in the Indian Ocean. <\/span>The resultant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a> created <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1933\">massive<\/a> waves as tall as 24 m (79 ft) when they reached the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3195\">shore<\/a> and killed more than an estimated 200,000 people along the Indian Ocean <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2890\">coastline<\/a>.<\/p>\n<p><b>Haiti (2010)<strong><span style=\"font-weight: 400\">\u2014<\/span><\/strong><\/b>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 7 earthquake that occurred on January 12, 2010, was followed by many <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3084\">aftershocks<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> 4.5 or higher. More than 200,000 people are estimated to have died as result of the earthquake. The widespread infrastructure damage and crowded conditions contributed to a cholera outbreak, which is estimated to have caused thousands more deaths.<\/p>\n<p><strong>T\u014dhoku, Japan (2011)<b><span style=\"font-weight: 400\">\u2014<\/span><\/b><\/strong>Because most Japanese buildings are designed to tolerate earthquakes, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">moment magnitude<\/a> 9.0 earthquake on March 11, 2011, was not as destructive as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunami<\/a> it created. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunami<\/a> caused more than 15,000 deaths and tens of billions of dollars in damage, including the destructive meltdown of the Fukushima nuclear power plant.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-65\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-65\" class=\"h5p-iframe\" data-content-id=\"65\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"9.9 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4316\" aria-describedby=\"caption-attachment-4316\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/9.9-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-665\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/9.9-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4316\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 9.9 via this QR Code.<\/figcaption><\/figure>\n<h2>Summary<\/h2>\n<p>Geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a>, applied force, comes in three types: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1445\">tension<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1447\">shear<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1446\">compression<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">Strain<\/a> is produced by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> and produces three types of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1448\">deformation<\/a>: elastic, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2582\">ductile<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2583\">brittle<\/a>. Geological maps are two-dimensional representations of surface <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2960\">formations<\/a> which are the surface expression of three-dimensional geologic structures in the subsurface. The map symbol called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1454\">dip<\/a> or rock attitude indicates the orientation of rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2857\">strata<\/a> with reference to north-south and horizontal. Folded rock layers are categorized by the orientation of their limbs, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1455\">fold<\/a> axes and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1456\">axial planes<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">Faults<\/a> result when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">stress<\/a> forces exceed rock integrity and friction, leading to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">brittle deformation<\/a> and breakage. The three major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3065\">fault<\/a> types are described by the movement of their fault blocks: normal, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3076\">strike-slip<\/a>, and reverse.<\/p>\n<p>Earthquakes, or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> activity, are caused by sudden <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1452\">brittle deformation<\/a> accompanied by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3079\">elastic rebound<\/a>. The release of energy from an earthquake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3080\">focus<\/a> is generated as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> waves. P and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3090\">S waves<\/a> travel through the Earth\u2019s interior. When they <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1453\">strike<\/a> the outer <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2580\">crust<\/a>, they create <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3089\">surface waves<\/a>. Human activities, such as mining and nuclear detonations, can also cause <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> activity. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">Seismographs<\/a> measure the energy released by an earthquake using a logarithmic scale of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a> units; the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3100\">Moment Magnitude<\/a> Scale has replaced the original <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3099\">Richter Scale<\/a>. Earthquake intensity is the perceived effects of ground shaking and physical damage. The location of earthquake foci is determined from triangulation readings from multiple <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a>.<\/p>\n<p>Earthquake rays passing through rocks of the Earth\u2019s interior and measured at the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3095\">seismographs<\/a> of the worldwide <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">Seismic<\/a> Network allow 3-D imaging of buried rock masses as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> tomographs.<\/p>\n<p>Earthquakes are associated with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2576\">plate tectonics<\/a>. They usually occur around the active <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2591\">plate<\/a> boundaries, including zones of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">subduction<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2620\">collision<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2601\">transform<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2599\">divergent<\/a> boundaries. Areas of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1183\">intraplate<\/a> earthquakes also occur. The damage caused by earthquakes depends on a number of factors, including <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3098\">magnitude<\/a>, location and direction, local conditions, building materials, intensity and duration, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3103\">resonance<\/a>. In addition to damage directly caused by ground shaking, secondary earthquake hazards include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3106\">liquefaction<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">tsunamis<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1199\">landslides<\/a>, seiches, and elevation changes.<\/p>\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n<div id=\"h5p-66\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-66\" class=\"h5p-iframe\" data-content-id=\"66\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Chapter 9 Review\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4294\" aria-describedby=\"caption-attachment-4294\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Ch.9-Review-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-666\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.9-Review-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4294\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the review quiz for Chapter 9 via this QR Code.<\/figcaption><\/figure>\n<h2>References<\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n<li class=\"csl-entry\">Christenson, G.E., 1995, The September 2, 1992 ML 5.8 St. George earthquake, Washington County, Utah: Utah Geological Survey Circular 88, 48 p.<\/li>\n<li class=\"csl-entry\">Coleman, J.L., and Cahan, S.M., 2012, Preliminary catalog of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1463\">sedimentary basins<\/a> of the United States: U.S. Geological Survey Open-File Report 1111, 27 p.<\/li>\n<li class=\"csl-entry\">Earle, S., 2015, Physical geology OER textbook: BC Campus OpenEd.<\/li>\n<li class=\"csl-entry\">Feldman, J., 2012, When the Mississippi Ran Backwards: Empire, Intrigue, Murder, and the New Madrid Earthquakes of 1811 and 1812: Free Press, 320 p.<\/li>\n<li class=\"csl-entry\">Fuller, M.L., 1912, The New Madrid earthquake: Central United States Earthquake Consortium Bulletin 494, 129 p.<\/li>\n<li class=\"csl-entry\">Gilbert, G.K., and Dutton, C.E., 1877, Report on the geology of the Henry Mountains: Washington, U.S. Government Printing Office, 160 p.<\/li>\n<li class=\"csl-entry\">Hildenbrand, T.G., and Hendricks, J.D., 1995, Geophysical setting of the Reelfoot <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2624\">rift<\/a> and relations between <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2624\">rift<\/a> structures and the New Madrid <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3087\">seismic<\/a> zone: U.S. Geological Survey Professional Paper 1538-E, 36 p.<\/li>\n<li class=\"csl-entry\">Means, W.D., 1976, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2915\">Stress<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2916\">Strain<\/a> &#8211; Basic Concepts of Continuum Mechanics: Berlin, Springe, 273 p.<\/li>\n<li class=\"csl-entry\">Ressetar, R. (Ed.), 2013, The San Rafael Swell and Henry Mountains <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_1461\">Basin<\/a>: geologic centerpiece of Utah: Utah Geological Association, Utah Geological Association, 250 p.<\/li>\n<li class=\"csl-entry\">Satake, K., and Atwater, B.F., 2007, Long-Term Perspectives on Giant Earthquakes and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3194\">Tsunamis<\/a> at <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_2602\">Subduction<\/a> Zones: Annual Review of Earth and Planetary Sciences, v. 35, no. 1, p. 349\u2013374., doi: <a href=\"https:\/\/doi.org\/10.1146\/annurev.earth.35.031306.140302\">10.1146\/annurev.earth.35.031306.140302<\/a>.<\/li>\n<li class=\"csl-entry\">Talwani, P., and Cox, J., 1985, Paleoseismic evidence for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_667_3104\">recurrence<\/a> of Earthquakes near Charleston, South Carolina: Science, v. 229, no. 4711, p. 379\u2013381.<\/li>\n<\/ol>\n<\/div>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_667_2915\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2915\"><div tabindex=\"-1\"><p>Force applied to an object, typically dealing with forces within the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2916\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2916\"><div tabindex=\"-1\"><p>The deformation that results from application of a stress.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2583\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2583\"><div tabindex=\"-1\"><p>A property of solids in which a force applied to an object causes the object to fracture, break, or snap. Most rocks, at low temperatures, are brittle.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2582\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2582\"><div tabindex=\"-1\"><p>A property of a solid, such that when a force is applied, the solid flows, stretches, or bends along with the force, instead of cracking or breaking. For example, many plastics are ductile.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1449\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1449\"><div tabindex=\"-1\"><p>A type of deformation that reverses when the stress is removed.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1453\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1453\"><div tabindex=\"-1\"><p>A measure of a geologic plane's orientation in 3-D space. Used for beds of rocks, faults, fold hinges, etc. Using the right hand rule, dip is perpendicular, and to the right 90\u00b0 of the strike.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1454\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1454\"><div tabindex=\"-1\"><p>A measure of a plane's (maximum) angle with respect to horizontal, where a perfectly horizontal plane has a dip of zero and a vertical plane has a dip of 90\u00b0.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2857\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2857\"><div tabindex=\"-1\"><p>Discernible layers of rock, typically from a sedimentary rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1455\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1455\"><div tabindex=\"-1\"><p>A rock layer that has been bent in a ductile way instead of breaking (as with faulting).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3065\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3065\"><div tabindex=\"-1\"><p>Planer feature where two blocks of bedrock move past each other via earthquakes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3079\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3079\"><div tabindex=\"-1\"><p>A theory of building energy that is released during an earthquake.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3087\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3087\"><div tabindex=\"-1\"><p>Energy that radiates from fault movement via earthquakes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3095\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3095\"><div tabindex=\"-1\"><p>Instrument used to measure seismic energy.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3098\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3098\"><div tabindex=\"-1\"><p>A measure of earthquake strength. Scales include Richter and Moment.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1448\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1448\"><div tabindex=\"-1\"><p>A strain that occurs in a substance in which the item changes shape due to a stress.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3383\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3383\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2675\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2675\"><div tabindex=\"-1\"><p>Rocks that are formed from liquid rock, i.e. from volcanic processes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1965\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1965\"><div tabindex=\"-1\"><p>A coherent body of intrusive rock (which formed underground) which is now at (or near) the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1934\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1934\"><div tabindex=\"-1\"><p>A break within a rock that has no relative movement between the sides. Caused by cooling, pressure release, tectonic forces, etc.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1447\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1447\"><div tabindex=\"-1\"><p>Stress within an object that causes a side-to-side movement within an internal fabric or weakness.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1452\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1452\"><div tabindex=\"-1\"><p>A style of strain in which an object suddenly breaks, fractures, or otherwise fails in a different way than ductile deformation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1445\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1445\"><div tabindex=\"-1\"><p>Stresses that pull objects apart into a larger surface area or volume; stretching forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1446\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1446\"><div tabindex=\"-1\"><p>Stresses that push objects together into a smaller surface area or volume; contracting forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2592\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2592\"><div tabindex=\"-1\"><p>Location where two plates are in contact, allowing a relative motion between the two plates. These are the locations where&nbsp;most earthquakes and volcanoes are found.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3081\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3081\"><div tabindex=\"-1\"><p>Amount of movement during a faulting event.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2599\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2599\"><div tabindex=\"-1\"><p>Place where two plates are moving apart, creating either a rift (continental lithosphere) or a mid-ocean ridge (oceanic lithosphere).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2600\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2600\"><div tabindex=\"-1\"><p>Place where two plates come together, casing subduction or collision.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2601\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2601\"><div tabindex=\"-1\"><p>Place where two plates slide past each other, creating strike slip faults.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3076\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3076\"><div tabindex=\"-1\"><p>Faulting that occurs with shear forces, typically on vertical fault plaines as two fault blocks slide past each other.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2931\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2931\"><div tabindex=\"-1\"><p>A separation of light (felsic) and dark (mafic) minerals in higher grade metamorphic rocks like gneiss.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1450\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1450\"><div tabindex=\"-1\"><p>A bending, squishing, or stretching style of deformation where an object changes shape smoothly.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1451\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1451\"><div tabindex=\"-1\"><p>An amount of strain where the substance has a maximum amount of elastic deformation and switches to ductile deformation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3116\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3116\"><div tabindex=\"-1\"><p>Empty space in a geologic material, either within sediments, or within rocks. Can be filled by air, water, or hydrocarbons.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2689\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2689\"><div tabindex=\"-1\"><p>The measure of the vibrational (kinetic) energy of a substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2917\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2917\"><div tabindex=\"-1\"><p>Non-directional pressure resulting from burial.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2678\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2678\"><div tabindex=\"-1\"><p>Pieces of rock that have been weathered and possibly eroded.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2839\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2839\"><div tabindex=\"-1\"><p>A very fine-grained rock with very thin layering (fissile).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1962\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1962\"><div tabindex=\"-1\"><p>General name of a felsic rock that is intrusive. Has more felsic minerals than mafic minerals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2960\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2960\"><div tabindex=\"-1\"><p>An extensive, distinct, and mapped set of geologic layers.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2192\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2192\"><div tabindex=\"-1\"><p>The third largest span of time recognized by geologists; smaller than a era, larger than a epoch. We are currently in the Quaternary period. Rocks of a specific period are called systems.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2858\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2858\"><div tabindex=\"-1\"><p>A specific layer of rock with identifiable properties.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1456\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1456\"><div tabindex=\"-1\"><p>Dividing two-dimensional line between the two sides of a fold.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1457\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1457\"><div tabindex=\"-1\"><p>Downward-facing fold, that has older rock in its core.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1458\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1458\"><div tabindex=\"-1\"><p>A U-shaped, upward-facing fold with younger rocks in its core.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1459\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1459\"><div tabindex=\"-1\"><p>A one-sided fold-like structure in which layers of rock warp upwards or downwards.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1460\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1460\"><div tabindex=\"-1\"><p>A rock up-warping of symmetrical anticlines.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1461\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1461\"><div tabindex=\"-1\"><p>A down-warped feature in the crust.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3338\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3338\"><div tabindex=\"-1\"><p>A dark liquid fossil fuel derived from petroleum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3342\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3342\"><div tabindex=\"-1\"><p>A geologic circumstance (such as a fold, fault, change in lithology, etc.) which allows petroleum resources to collect.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3183\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3183\"><div tabindex=\"-1\"><p>Bottommost part of a wave.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2898\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2898\"><div tabindex=\"-1\"><p>A topographic high found away from the beach in deeper water, but still on the continental shelf. Typically, these are formed in tropical areas by organisms such as corals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3073\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3073\"><div tabindex=\"-1\"><p>A dip-slip fault that has the hanging wall moving up with respect to the foot wall.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1463\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1463\"><div tabindex=\"-1\"><p>A local or regional depression which allows sediments to accumulate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1464\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1464\"><div tabindex=\"-1\"><p>The act of the land surface down-warping, typically referred to when discussing sedimentation or with rapid groundwater removal.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1428\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1428\"><div tabindex=\"-1\"><p>The last period of the Paleozoic, 299-252 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2852\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2852\"><div tabindex=\"-1\"><p>Adjective for a rock filled with fossils, most commonly with limestones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2834\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2834\"><div tabindex=\"-1\"><p>A rock primarily made of sand.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2851\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2851\"><div tabindex=\"-1\"><p>A chemical or biochemical rock made of mainly calcite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2580\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2580\"><div tabindex=\"-1\"><p>The outermost chemical layer of the Earth, defined by its low density and higher concentrations of lighter elements. The crust has two types: <strong>continental<\/strong>, which is the thick, more ductile, and lowest density, and <strong>oceanic<\/strong>, which is higher density, more brittle, and thinner.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3066\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3066\"><div tabindex=\"-1\"><p>Faulting that occurs with a vertical motion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3067\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3067\"><div tabindex=\"-1\"><p>On a dipping fault, the side that is on top of the fault plane. Moves down in normal faulting, up in reverse faulting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3068\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3068\"><div tabindex=\"-1\"><p>On a dipping fault, the part of the block that is below the fault. Moves down in normal faulting, up in reverse faulting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2664\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2664\"><div tabindex=\"-1\"><p>An interconnected set of parts that combine and make up a whole.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3324\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3324\"><div tabindex=\"-1\"><p>Place where material is extracted from the Earth for human use.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2591\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2591\"><div tabindex=\"-1\"><p>A solid part&nbsp;of the lithosphere which moves as a unit, i.e. the entire plate generally moves the same direction at the same speed.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3107\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3107\"><div tabindex=\"-1\"><p>Place where fault movement cuts the surface of the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3069\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3069\"><div tabindex=\"-1\"><p>A polished surface of rock from fault movement, covered with groves.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2462\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2462\"><div tabindex=\"-1\"><p>Term for the extensional tectonic province that extends from California's Sierra Nevada Mountains in the west, to Utah's Wasatch Mountains to the east, to southern Oregon and Idaho to the north, to northern Mexico to the south. Known as a wide rift, as each graben 'basin,' bounded by horst 'ranges.' Each set of horsts with a graben has some individual extension, adding up to the overall rifting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2626\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2626\"><div tabindex=\"-1\"><p>A valley formed by normal faulting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2625\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2625\"><div tabindex=\"-1\"><p>Uplifted mountain block caused by normal faulting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3071\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3071\"><div tabindex=\"-1\"><p>A valley formed by normal faulting on just one side.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3070\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3070\"><div tabindex=\"-1\"><p>A dip-slip fault in which the hanging wall drops relative to the footwall, caused by extensional forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2586\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2586\"><div tabindex=\"-1\"><p>Middle chemical layer of the Earth, made of mainly iron and magnesium silicates. It is generally denser than the crust (except for older oceanic crust) and less dense than the core.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3074\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3074\"><div tabindex=\"-1\"><p>A low-angle reverse fault, common in mountain building.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2859\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2859\"><div tabindex=\"-1\"><p>The study of rock layers and their relationships to each other within a specific area.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2602\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2602\"><div tabindex=\"-1\"><p>A process where an oceanic plate descends bellow a less dense plate, causing the removal of the plate from the surface. Subduction causes the largest earthquakes possible, as the subducting plate can lock as it goes down. Volcanism is also caused as the plate releases volatiles into the mantle, causing melting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3075\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3075\"><div tabindex=\"-1\"><p>Term for faulting that occurs in subduction.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2581\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2581\"><div tabindex=\"-1\"><p>The thin, outer layer of the Earth which makes up the rocky bottom of the ocean basins. It is made of rocks similar to basalt, and as it cools, even become more dense than the upper mantle below.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1933\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1933\"><div tabindex=\"-1\"><p>A feature with no internal structure, habit, or layering.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3194\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3194\"><div tabindex=\"-1\"><p>Formally known as a tidal wave, it is a large wave produced from a sudden movement of the floor of a ocean basin, caused by events such as earthquakes, volcanic eruptions, landslides, and bolide impacts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2630\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2630\"><div tabindex=\"-1\"><p>A divergent boundary within an oceanic plate, where new lithosphere and crust is created as the two plates spread apart. Mid-ocean ridge and spreading center are synonyms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2632\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2632\"><div tabindex=\"-1\"><p>A strike-slip or transform motion in which the relative motion is to the left. As viewed across the fault, objects will move to the left.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3077\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3077\"><div tabindex=\"-1\"><p>Movement in a transform or strike-slip setting which it toward the right across the fault.&nbsp;As viewed across the fault, objects will move to the right.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2634\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2634\"><div tabindex=\"-1\"><p>A segment along a transform or strike-slip fault which has a compressional component, sometimes creating related thrust faulting and mountains.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2635\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2635\"><div tabindex=\"-1\"><p>A place along a transform or strike-slip fault with an extensional component, sometimes including normal faulting, basin formation, and volcanism.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3078\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3078\"><div tabindex=\"-1\"><p>A small area along a strike-slip or transform fault with branching structures of transpression\/transtension, causing local hills or valleys.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1183\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1183\"><div tabindex=\"-1\"><p>Activities that occur within plates, away from plate boundaries.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2655\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2655\"><div tabindex=\"-1\"><p>An accepted scientific idea that explains a process using the best available information.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3080\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3080\"><div tabindex=\"-1\"><p>Initiation point of an earthquake or fault movement.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2447\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2447\"><div tabindex=\"-1\"><p>A slow and steady movement. Used with faults, mass wasting in soils, and grain movement.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3082\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3082\"><div tabindex=\"-1\"><p>An earthquake that sometimes occurs before the larger mainshock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3083\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3083\"><div tabindex=\"-1\"><p>Largest earthquake in an earthquake sequence.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3084\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3084\"><div tabindex=\"-1\"><p>Earthquake(s) that occur after the mainshock, usually decreasing in amount and magnitude over time.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3085\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3085\"><div tabindex=\"-1\"><p>The location at the surface directly above the focus of an earthquake, typically associated with strong damage.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3184\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3184\"><div tabindex=\"-1\"><p>Height or depth of a wave from the middle point.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3186\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3186\"><div tabindex=\"-1\"><p>The distance between any two repeating portions of a wave (e.g., two successive wave crests).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3088\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3088\"><div tabindex=\"-1\"><p>Seismic waves that travel through the Earth, mainly P waves and S waves.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3089\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3089\"><div tabindex=\"-1\"><p>Seismic waves that only move along the surface, mainly R waves and L waves.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3086\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3086\"><div tabindex=\"-1\"><p>The fastest seismic wave that occurs after an earthquake, compressional in nature.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3090\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3090\"><div tabindex=\"-1\"><p>Second-fastest seismic wave that has a sheer motion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3091\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3091\"><div tabindex=\"-1\"><p>Waves that change direction due to changing speeds, typically caused by a change in density of the medium.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3092\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3092\"><div tabindex=\"-1\"><p>Surface waves that have a side-to-side motion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3093\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3093\"><div tabindex=\"-1\"><p>Surface waves that have a up and down motion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2595\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2595\"><div tabindex=\"-1\"><p>The outer physical&nbsp;layer of the core, which is liquid. Movement within the outer core is believed to be responsible for Earth's magnetic field and flips of the magnetic field.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2589\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2589\"><div tabindex=\"-1\"><p>The innermost chemical layer of the Earth, made chiefly of iron and nickel. It has both liquid and solid components.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3109\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3109\"><div tabindex=\"-1\"><p>Earthquakes that occur due to human activity.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3339\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3339\"><div tabindex=\"-1\"><p>Gaseous fossil fuel derived from petroleum, mostly made of methane.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3108\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3108\"><div tabindex=\"-1\"><p>A process of injecting pressurized fluids into the ground to aid in hydrocarbon migration.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3100\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3100\"><div tabindex=\"-1\"><p>A magnitude scale based on calculation of the energy released in an earthquake.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3174\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3174\"><div tabindex=\"-1\"><p>A place where pressurized groundwater flows onto the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3096\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3096\"><div tabindex=\"-1\"><p>A process of using 3D seismic arrays to get subsurface images.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3097\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3097\"><div tabindex=\"-1\"><p>Areas that have an unpredicted change in seismic data, indicating a change in properties.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2576\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2576\"><div tabindex=\"-1\"><p>The theory that the outer layer of the Earth (the lithosphere) is broken in several plates, and these plates move relative to one another, causing the major topographic features of Earth (e.g. mountains, oceans) and most earthquakes and volcanoes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1185\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1185\"><div tabindex=\"-1\"><p>A reservoir of magma below a volcano.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2638\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2638\"><div tabindex=\"-1\"><p>Rising stationary magma, forming a succession of volcanism. This is reflected as islands on oceanic plates, and volcanic mountains or craters on land.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2575\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2575\"><div tabindex=\"-1\"><p>The layers of igneous, sedimentary, and metamorphic rocks that form the continents. Continental crust is much thicker than oceanic crust. Continental crust is defined as having higher concentrations of&nbsp;very light elements like K, Na, and Ca, and is the lowest density rocky layer of Earth. Its average composition is similar to granite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3099\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3099\"><div tabindex=\"-1\"><p>A magnitude scale using the amplitude of shaking via a seismograph.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3101\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3101\"><div tabindex=\"-1\"><p>A qualitative earthquake scale, from I-XII, of the degree of shaking in an earthquake.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2647\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2647\"><div tabindex=\"-1\"><p>An observation which is based on non-numerical data. While these types of observations are not preferred, they can still be useful.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2646\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2646\"><div tabindex=\"-1\"><p>An observation which is based on numerical data. These observations are preferred because they can be used in calculations.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2914\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2914\"><div tabindex=\"-1\"><p>Rocks and minerals that change within the Earth are called metamorphic, changed by heat and pressure. Metamorphism is the name of the process.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1971\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1971\"><div tabindex=\"-1\"><p>Term for the underlying lithified rocks that make up the geologic record in an area. This term can sometimes refer to only the deeper, crystalline (non-layered) rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3187\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3187\"><div tabindex=\"-1\"><p>Speed at which a wave travels past a fixed point.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3103\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3103\"><div tabindex=\"-1\"><p>An amplification of earthquake waves due to a structure of buildings or structures.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3104\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3104\"><div tabindex=\"-1\"><p>Average time between earthquakes calculated based on past earthquake records.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1181\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1181\"><div tabindex=\"-1\"><p>Place where lava is erupted at the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2890\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2890\"><div tabindex=\"-1\"><p>The entire area which is related to land-sea interactions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2620\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2620\"><div tabindex=\"-1\"><p>When two continents crash, with no subduction (and thus little to no volcanism), since each continent is to buoyant. Many of the largest mountain ranges and broadest zones of seismic activity come from collisions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2624\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2624\"><div tabindex=\"-1\"><p>Area of extended continental lithosphere, forming a depression. Rifts can be narrow (focused in one place) or broad (spread out over a large area with&nbsp;many faults).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3333\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3333\"><div tabindex=\"-1\"><p>A mechanical process which takes ore and separates it from gangue material.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2918\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2918\"><div tabindex=\"-1\"><p>Stress that has a strong directional component (unequal), typically creating elongated or flattened features.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3106\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3106\"><div tabindex=\"-1\"><p>Process of saturated sediments becoming internally weak (like quicksand) and destabilizing foundations.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2706\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2706\"><div tabindex=\"-1\"><p>A solution that has the maximum allowed dissolved component, and is unable to dissolve more.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2692\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2692\"><div tabindex=\"-1\"><p>Forces that hold a substance together.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_1199\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_1199\"><div tabindex=\"-1\"><p>General term for sudden material falling down a slope due to gravity. The term can sometimes cover a wide range of events, including debris flows, rock falls, and mudslides.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3195\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3195\"><div tabindex=\"-1\"><p>The part of the coastline which is directly related to water-land interaction, specifically the tidal zone and the range of wave base.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3182\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3182\"><div tabindex=\"-1\"><p>Top of a wave.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3117\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3117\"><div tabindex=\"-1\"><p>An event that causes a landslide event. Water is a common trigger.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3134\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3134\"><div tabindex=\"-1\"><p>A channelled body of water.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3366\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3366\"><div tabindex=\"-1\"><p>The most recent supercontinent, which formed over 300 million years ago and started breaking apart less than 200 million years ago. Africa and South America, as well as Europe and North America, bordered each other.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_3110\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_3110\"><div tabindex=\"-1\"><p>Any downhill movement of material, caused by gravity.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_667_2909\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_667_2909\"><div tabindex=\"-1\"><p>Wind-blown silt, mainly formed from glacial processes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":83,"menu_order":9,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-667","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":19,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/667","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/users\/83"}],"version-history":[{"count":3,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/667\/revisions"}],"predecessor-version":[{"id":3410,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/667\/revisions\/3410"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/parts\/19"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/667\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/media?parent=667"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapter-type?post=667"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/contributor?post=667"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/license?post=667"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}