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Davis, California

Tuesday, October 26, 2021

The shaky reality of living in California

CINDY CHEUNG / AGGIE
CINDY CHEUNG / AGGIE

UC Davis researchers discuss implications, Southern California earthquake advisory

A Southern California earthquake advisory from the California Office of Emergency Services (Cal OES) shook the nerves of the public all across social media from Sept. 30 to Oct. 4. The advisory reminded all California residents of the potential dangers of a large earthquake affecting urban areas, including Davis.

“Warnings are usually fairly cautious in their language in order to avoid inciting chaos,” UC Davis professor emeritus Donald Turcotte said. “Uncertainties are so great because the chances are one in 100, but the risk is always there. So warnings are given out just in case.”

For Turcotte, the advisory was more precautionary than anything else. For California, where public knowledge of local earthquakes is widespread, a warning based on a wild guess is better than none at all.

“There is always a risk in trying this information [on] the public because people don’t deal well with low-probability issues,” said geology professor Michael Oskin. “They tend to overemphasize [the probability of an earthquake], and it does not help that some news organizations are only seeking publicity for themselves and will hype things. The reality of [the warning] was that [there] was an enhanced chance [of an earthquake] over the long-term.”

Cal OES issued the advisory due to concerns that an earthquake near the San Andreas Fault would trigger a larger earthquake as a part of an “earthquake swarm.”

According to James McClain, a professor in the Earth and Planetary Sciences, his department defines an earthquake swarm as an unusually large number of earthquakes, densely packed over a short period of time. This occurs when one fault may be slipping, or a number of closely spaced faults are slipping slightly.

This particular San Andreas swarm took place near the Salton Sea. The concern was that it would trigger an even larger earthquake along the San Andreas Fault. The advisory is no longer in place, meaning that, for the moment, there is no longer an increased probability of an earthquake happening along the fault.

“There is an increased probability of an earthquake during one of these swarms […] but probability is not stationary,” Oskin said. “We don’t understand earthquakes sufficiently [enough] to say ‘yes’ or ‘no’ if something is going to trigger an earthquake. There are times where earthquake activity is enhanced, and we should be more wary of other things happening. It is not like forecasting the weather yet.”

California has multiple faults that are cause for concern when it comes to earthquakes. However, the impact of earthquakes on certain faults varies throughout the state.

The San Andreas Fault in Southern California is under the most surveillance by seismologists since it is due for an earthquake. According to McClain, the Hayward Fault in the East Bay is the nearest fault to Davis that is due for an earthquake.

“Every part of California has some sort of earthquake potential that people should be concerned about,” McClain said. “However, we do not have to worry about [how a] Southern California [earthquake could affect us], and they do not have to worry about a big earthquake here.”

The concern for this advisory was in the increased probability of a quake occurring along a fault that is due for an earthquake. Earthquakes tend to happen along the San Andreas about once every 300 years, according to Oskin. So, in a year, the probability of an earthquake is one in 300 and one in 10,000 every day. During this swarm, the probability went from one in 10,000 to one in 100, which warranted the advisory.

“During this swarm the likelihood increased by a factor of 100,” Oskin said. “It is still a 1 percent chance that the earthquake [could be] the next day. That level of change in probability from very small numbers to another very small number [causes] a very big relative increase.”

Since Davis is rather far away from the coast, the city would not be as affected by a large earthquake on the Hayward Fault as it would be by its after-effects. So, for Oskin, remaining prepared for the possibility of a large earthquake is a vital aspect of living in this state.

He suggested that Davis citizens stay informed of building codes for earthquakes and make sure the contents of their homes are firmly screwed down to avoid getting hit by something falling during a quake.

“We haven’t had a very large earthquake in California in more than two decades that has affected urban regions, [but] it is good to be reminded that we have a very large earthquake hazard in California,” Oskin said. “Maybe this particular reminder was a little bit overblown […]  but there is a benefit to reminding people of the hazard that they should prepare for.”
Written by: Amanda Cruz — features@theaggie.org

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