{"id":465,"date":"2021-09-16T19:29:46","date_gmt":"2021-09-16T19:29:46","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/physicalgeology\/chapter\/12-4-measuring-geological-structures-physical-geology-2nd-edition\/"},"modified":"2021-09-16T19:43:11","modified_gmt":"2021-09-16T19:43:11","slug":"12-4-measuring-geological-structures-physical-geology-2nd-edition","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/physicalgeology\/chapter\/12-4-measuring-geological-structures-physical-geology-2nd-edition\/","title":{"raw":"12.4 Measuring Geological Structures -- Physical Geology – 2nd Edition","rendered":"12.4 Measuring Geological Structures — Physical Geology – 2nd Edition"},"content":{"raw":"\n\n
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Figure 12.4.1  A depiction of the strike and dip of some tilted sedimentary beds.  The dipping beds are shown partially covered with water so that you can visualize a horizontal line on the rock surface. The notation for expressing strike and dip on a map is also shown.<\/div>\n <\/div>\n

Measurement of geological features is done with a special compass that has a built-in clinometer\u2014a device for measuring vertical angles. An example of how this is done is shown on Figure 12.4.2.<\/p>\n

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Figure 12.4.2 Measuring the compass direction of the strike (left) and the vertical angle of the dip (right) using a compass with a clinometer.<\/div>\n <\/div>\n

Strike and dip are also used to describe any other planar features, including joints, faults, dykes, sills, and even the foliation planes in metamorphic rocks. Figure 12.4.3 shows an example of how we would depict the beds that make up an anticline on a map.<\/p>\n

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Figure 12.4.3 A depiction of an antiform and a dyke in cross-section (looking from the side) and in map view (a.k.a. plan view) with the appropriate strike-dip and antiform symbols.<\/div>\n <\/div>\n

The beds on the west (left) side of the map are dipping at various angles to the west. The beds on the east side are dipping to the east. The middle bed (light grey) is horizontal; this is denoted by a cross within a circle. The dyke is dipping at 80\u02da to the west. The hinge of the fold is denoted with a dashed line with two arrows that point away from it.  If it was a synform, the arrows would point towards the line.<\/p>\n

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This cross-section shows seven tilted sedimentary layers (a to g), a fault, and a steeply dipping dyke. Place strike and dip symbols on the map to indicate the orientations of the beds shown, the fault, and the dyke. Then answer the questions.<\/p>\n

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  1. What type of fault is this, and is this an extensional or compressional situation?<\/li>\n
  2. What are the relative ages of the nine geological features shown here (seven beds, dyke, and fault)? Which are the youngest and oldest?<\/li>\n <\/ol>\n

    See Appendix 3 for Exercise 12.3 answers<\/a>.<\/p>\n <\/div>\n <\/div>\n

    Media Attributions<\/h3>\n