Figure 11.5.1 Earthquakes on the Parkfield segment of the San Andreas Fault between 1881 and 2004.

The U.S. Geological Survey recognized this as an excellent opportunity to understand earthquakes and earthquake prediction, so they armed the Parkfield area with a huge array of geophysical instruments and waited for the next quake, which was expected to happen around 1987. Nothing happened! The “1987 Parkfield earthquake” finally struck in September 2004. Fortunately all of the equipment was still there, but it was no help from the perspective of earthquake prediction. There were no significant precursors to the 2004 Parkfield earthquake in any of the parameters measured, including seismicity, harmonic tremor, strain (rock deformation), magnetic field, the conductivity of the rock, or creep, and there was no foreshock. In other words, even though every available technique was used to monitor it, the 2004 earthquake came as a complete surprise, with no warning whatsoever.

Figure 11.5.2 Probabilities of a M6.7 or larger earthquake over the period 2014 to 2043 on various faults in the San Francisco Bay region of California.

The hope for earthquake prediction is not dead, but it was hit hard by the Parkfield experiment. The current focus in earthquake-prone regions is to provide forecasts of the probability of an earthquake of a certain magnitude within a certain time period—typically a number of decades—while officials focus on ensuring that the population is educated about earthquake risks and that buildings and other infrastructure are as safe as can be. An example of this approach for the San Francisco Bay region of California is shown in Figure 11.5.2. Based on a wide range of information, including past earthquake history, accumulated stress from plate movement, and known stress transfer, seismologists and geologists have predicted the likelihood of a M6.7 or greater earthquake on each of eight major faults that cut through the region. The greatest probabilities are on the Hayward, Rogers Creek, Calaveras, and San Andreas Faults. As shown in Figure 11.5.2, there is a 72% chance that a major and damaging earthquake will take place somewhere in the region prior to 2043.

As we’ve discussed already, it’s not sufficient to have strong building codes, they have to be enforced. Building code compliance is quite robust in most developed countries, but is sadly inadequate in many developing countries.

It’s also not enough just to focus on new buildings; we have to make sure that existing buildings—especially schools and hospitals—and other structures such as bridges and dams, are as safe as they can be. An example of how this is applied to schools in B.C. is described in Exercise 11.5.

Making the Seismic Upgrade in B.C.’s Schools

British Columbia is in the middle of a multi-billion-dollar program to make schools safer for students. The program is focused on older schools, because, according to the government, those built since 1992 already comply with modern seismic codes. Some schools would require too much work to make upgrading economically feasible and they are slowly being replaced. Where upgrading is feasible, the school is assessed carefully before any upgrade work is initiated.

An example is Sangster Elementary in Colwood on southern Vancouver Island. The school was originally built in 1957, with a major addition in 1973. Ironically, the newer part of the school, built of concrete blocks, required strengthening with the addition of a steel framework, while the 1957 part, which is a wood-frame building, did not require seismic upgrading. The work was completed in 2014.

Figure 11.5.3 Sangster Elementary image from Google Maps – street view.

As of July 2019, upgrades had been completed at 168 B.C. schools, 17 were underway, and an additional 26 were ready to proceed, with funding identified. Another 274 schools were listed as needing upgrades.^[1]

The final part of earthquake preparedness involves the formulation of public emergency plans, including escape routes, medical facilities, shelters, and food and water supplies. It also includes personal planning, such as emergency supplies (food, water, shelter, and warmth), escape routes from houses and offices, and communication strategies (with a focus on ones that don’t involve the cellular network).

Media Attributions

• Figure 11.5.1: © Steven Earle. CC BY.
• Figure 11.5.2: “San Francisco Bay region Earthquake Probability [PDF]” by USGS. Public domain.
• Figure 11.5.3: Sangster Elementary school. © 2018 Google Maps. Street View. See Google’s permissions for non-commercial use. 

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