Shakeout: Preparing for the next great California earthquake

Graphic by Jordan Wong

It’s not a question of “if,” but “when.”

Southern California is overdue for a large earthquake. Scientists have determined that the likelihood of a magnitude 7.5 or greater earthquake, occurring in the next 30 years, is 46 percent. The chance of a 6.7 magnitude or higher earthquake is over 99 percent.

It is imperative we plan now for the inevitable.

Each year, citizens across the state of California participate in the Great California Shakeout, an earthquake drill initiated as a result of “The Shakeout Scenario,” a study published in 2008.

Dr. Linda Reinen, a structural geologist and Pomona College geology professor, gives an annual lecture on the shakeout scenario and earthquake preparedness.

Southern California lies on a transform plate boundary, where two tectonic plates, the Pacific plate to the west and the North American plate to the east, slide past each other, Reinen outlined. A number of faults in the region accommodate this movement.

Reinen explained that the primary fault in Southern California is the San Andreas Fault. As the plates move past each other, friction creates resistance to the movement, resulting in a build-up of stress.  

Eventually, “the stresses get so high, the frictional resistance is overcome; the plates slide past one another, and we get an earthquake,” Reinen said.

The three most recent major earthquakes on the San Andreas include a rupture on the northern section of the fault in 1906 (the earthquake and subsequent fire that destroyed San Francisco), an 1857 earthquake on a section that runs just behind Claremont, and a 1680 rupture on the southern section of the fault.

“You can dig back [deep in] time and look at disturbed layers and find out when these faults have ruptured before,” Reinen said. “It turns out that each one of these sections, roughly, has a large earthquake every 100 to 150 years.”

She added that it has been more than 300 years since a large earthquake has occurred on the Southern section, meaning a large earthquake is overdue.

Since the southern section and the section of the fault closest to Claremont are primed and ready for movement, Reinen said that it’s widely believed to be the location of the next major earthquake, and when it does, it will affect all of Southern California.

The Shakeout Scenario was conducted by a team of over 200 organizations and researchers, who sought out to understand the “physical, social and economic consequences of a major earthquake in [S]outhern California.”

The study modeled the probable scenario of a magnitude 7.8 earthquake on the southernmost 300 kilometers of the San Andreas Fault.

It was not the biggest possible earthquake, or the worst one. It was just a reasonable earthquake based on “where previous earthquakes have happened, how much slip was accommodated (how much stress was relieved), and the type of materials situated along the fault,” Reinen said.

The study was an interdisciplinary endeavor. Information on earthquake behavior was passed from geoscientists to engineers, who analyzed what type of buildings could withstand the estimated shaking. That data was then given to social scientists who determined the social response to the potential infrastructure damage.

All of this information was then given to policymakers “who can affect change now before the earthquake happens [in order] to minimize effects,” Reinen said.

“The shakeout drills are done as a way for us, the community, to test communications, to test evacuations, and to test the preparedness of emergency responders across the region,” Reinen added. She explained that some of the first findings that came out of the study were that communications ended at political boundaries.

“For example, San Bernardino County might have empty hospitals and Los Angeles County might have overflowing hospitals, and that kind of [cross] communication was not happening,” Reinen said.

What should students do to prepare for an earthquake? Reinen advises every student to have a go-bag that contains food, water, medical supplies, etc. If you wear contacts, make sure to have an extra pair of glasses on hand.

“After the Northridge earthquake, two of the most common requests … were for glasses and tennis shoes,” Reinen said.

Also, make sure you keep a pair of shoes by your bed. The earthquake may break windows and it’s advisable to wear shoes when walking through the broken glass.

During the earthquake, “drop, cover, and hold on. Stay under for probably a minute or more after the shaking stops … to make sure that there is not another earthquake coming right after,” Reinen said. Running out of the building is ill-advised, as the shaking can throw people to the ground, making them more susceptible to injury.

Then, in the aftermath, plan to assist the community, she advised.

“One of the things that came out of the study was that people should be planning to be rescuers and not necessarily count on emergency responder services because if this disaster is like previous disasters that have happened in the past, about 95 percent of the rescues are from fellow victims as opposed to emergency personnel,” Reinen said.

Reinen also suggested identifying a person outside the region who would be able to contact all your friends and family for you.

“If this is like other earthquakes that have happened, phone calls don’t get out because the systems are overloaded,” Reinen said. “But, text messages are usually able to.”

Whether it occurs tomorrow, or 60 years from now, the “Big One” is inevitable. Planning, preparation, and practice are imperative.

If you have any other questions or just want to learn more about the shakeout scenario, California’s tectonic landscape, or earthquake preparedness, Reinen will be giving her annual talk Oct. 17 at SCC Room 201.

D’Maia Curry is a geology major at Pomona College. She loves dancing, reading, and looking at really cool rocks.

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