California bracing for the ‘Big One’? Experts weigh in as earthquake swarm hits for 4th day in a row

California has been hit by an earthquake swarm for the fourth day in a row. Residents have been experiencing earthquake swarms for nearly a week, with the latest hitting on Tuesday, December 16. The US Geological Survey (USGS) reported that a quake with a 3.1-magnitude happened near San Ramon, the epicenter of the recent seismic activity, at 5.53am PT (8.53am ET). This was followed by a dozen smaller quakes ranging from 1.1 to 1.6 magnitude, according to the Daily Mail.

Meanwhile, an expert has warned that there is a 72% chance of the Big One hitting between now and 2043, the outlet reported.

San Ramon has been hit by multiple quakes over the past four days, including magnitudes 2.9, 2.3, and 2.2 on December 13, a 2.8-magnitude quake on December 14 and 2.4 and 2.1 on December 15. There were dozens of other smaller tremors.

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At least 21 earthquakes ranging from magnitude 2.9 to 4.0 have rocked San Ramon over the past two months, USGS data revealed. The city recorded at least 90 earthquakes in the last month alone, but most of them were too small to cause any damage.

Residents were alarmed by the uptick in seismic activity, with some wondering if this could be a warning sign for a larger quake. However, experts do not think so.

USGS research geophysicist Annemarie Baltay said she does not believe that these tremors are a reason for unusual concern, and that they do not indicate that anything larger will affect San Ramon. “These small events, as all small events are, are not indicative of an impending large earthquake,” Baltay told Patch.

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“However, we live in earthquake country, so we should always be prepared for a large event,” she added. “There is a 72 percent chance of a magnitude 6.7 or larger earthquake occurring anywhere in the Bay Area between now and 2043. So we should all be aware and be prepared.”

Records from the USGS showed that there were similar earthquake swarms in 1970, 1976, 2002, 2003, 2015 and 2018.

Sarah Minson, a research geophysicist with the USGS's Earthquake Science Center at California's Moffett Field, told SF Gate, “This has happened many times before here in the past, and there were no big earthquakes that followed. We think that this place keeps having earthquake swarms due to a lot of fluid-filled cracks, thanks to very complex fault geometry, unlike, say, the San Andreas Fault, which is this nice clean edge.”

Seismic activity in San Ramon began in early November with a 3.8 magnitude. Since then, the tremors have continued.

Roland Burgmann, a UC Berkeley seismologist, told SFGATE that since the first quake in November was the strongest, it is possible that the whole series is not just a swarm, but a tense aftershock sequence.

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