Scientists debate earthquake risk

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Author: Donovan Dennis

A recent study predicting a 99.9 percent chance of a major earthquake in Southern California has Angelenos shaking — some shaking their heads — at the risk of the next great quake.

The study, authored by NASA-Jet Propulsion Laboratory Scientist Andrea Donnellan and colleagues, predicts a 5.0 or larger earthquake within the 60-mile radius of the 2014 earthquake on the Puente Hills fault in La Habra, California. The authors suggest an almost certain chance it could occur between April 1, 2015, and April 1, 2018 — a prediction that has many other scientists, including those at the U.S. Geological Survey (USGS), raising eyebrows.

In a statement released Oct. 20, the USGS took the uncharacteristic step of questioning the scientific accuracy of the Donnellan predictions.

“The earthquake rate implied by the 99.9 percent probability is significantly higher than observed at any time previously in Southern California, and the lack of details on the method of analysis makes a critical assessment of this approach very difficult,” USGS officials said in the statement published online. “Therefore, the USGS does not consider the analysis presented in this paper a reason to change our assessment of the hazard.”

The USGS-accepted model “UCERF3” gives a 3-year earthquake probability of 85 percent, which contrasts with the prediction offered by Donnellan. Both, however, suggest a high possibility of an earthquake in Southern California within the next several years.

“The community agrees we will probably have a 5.0 in the next three years — a 5.0 is not very big,” Occidental Geology Professor Ann Blythe said. “But to quantify it at 99.9 percent is ridiculous.”

A 2014 study by the University of California, Berkeley identifies two addresses for buildings on Occidental’s campus as potential at-risk buildings: 1600 Campus Road and 1824 Campus Road — the Childhood Development Center. The study’s authors are careful to emphasize that determining the true risk for every address listed requires further investigation by structural engineers and that the list includes all concrete buildings constructed after 1976.

“Appearing on the list has more to do with broad categories such as age and construction type,” Director of Facilities Tom Polansky said via email. “We hired the structural engineering firm of John A. Martin & Associates earlier this year to do a seismic survey of campus buildings. That survey found that the overall life safety risk at Oxy is low.”

Published by the Los Angeles Times, the 2014 list identified 1,500 concrete buildings in LA whose construction materials indicate an increased risk of collapsing. Because non-retrofitted concrete walls tend to crumble instead of cracking or dispersing the energy like wood frames, reinforced concrete buildings have historically “pancaked” under extreme shaking.

The paper preceded new building code and retrofitting laws written by LA Mayor Eric Garcetti in consultation with the USGS and other scientists. The ordinance, passed unanimously by the LA City Council Oct. 9, targets wood-frame apartment complexes and brittle concrete buildings throughout the city. Current estimates suggest approximately 15,000 structures now require retrofitting, and lawmakers are currently working with building owners to find subsidies for renovations.

Students concerned about the next “big one” — generally considered between 6.5 to 7.0 magnitude — in LA should not live in fear, Blythe said. She noted that it is important to not only be aware of the risks associated with living in a seismically active area, but also know how to minimize their potential impact.

Tom Mirovski (senior), who has lived in Southern California his entire life, expressed little concern about earthquakes in the region.

“I guess they’re not frequent enough to warrant concern,” Mirovski said. “I’ve never really experienced a big earthquake here.”

Water will be the scarcest resource in the wake of a large earthquake. A 7.0 or greater magnitude earthquake on the southern San Andreas fault has the potential to rupture the California and Colorado River aqueducts that cross the fault in several locations on their route to Southern California. Major freeways, too, will be impacted, Blythe said. Interstates 5, 15, 210 and 10 — all major highways connecting Southern California to cities north and east — cross the San Andreas.

“Thirty meters of displacement is a reasonable estimate for a rupture on the southern San Andreas,” Blythe said. “It may be possible for cars to roughly connect and get through, but it will be hard to get traffic flowing.”

Blythe recommends students be prepared for earthquakes by making an emergency plan that includes designating someone outside California as a point of contact in case of an emergency. Because communications may be unreliable in the immediate hours or days after a large earthquake, choosing one person to inform other family and friends could alleviate the need to make multiple calls. Additionally, she recommends students maintain at least several days to one week’s supply of drinking water in their rooms or vehicles at all times.

In addition to emergency supplies in students’ rooms, the college maintains a permanent supply of emergency water and food provisions, including over 6,000 gallons of water at various locations across campus, according to Environmental Health and Safety Manager Bruce Steele.

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