Brace Yourself: More Quakes Expected to Follow Monday's Swarm

PASADENA, CA - A swarm of earthquakes struck the Salton Sea in Imperial County today, the U.S. Geological Survey reported, with numerous aftershocks expected over the next few days.

The largest, a pair of magnitude-4.3 quakes that struck at 7:31 a.m. and 8:23 p.m., were among just over 100 events measured at the lake, just south of the Riverside County border.

According to the U.S. Geological Survey, a quake epicentered in the Salton Sea area would send some of the hardest jolts to the Coachella Valley region and East Los Angeles where loose sediment ensures residents could endure a full two minutes of hard shaking. Earthquake simulations show several densely populated areas that would be hit hardest if the Big One strikes.

Monday's quakes ranged from magnitude 1.4 to the 4.3-magnitude quakes during the swarm that began at 4:03 a.m., according to Jennifer Andrews of the Caltech Seismological Laboratory.

A magnitude-4.2 earthquake struck at 8:36 p.m., Andrews said.

The swarm pattern differs from a larger single event that is preceded and followed by smaller quakes, Andrews said.

"We're referring to this as a swarm ... not just one huge event," she told City News Service. "We've recorded just over 100 events since this morning."

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Andrews said it is difficult to estimate the chances of a larger event occurring as the swarm continues, but added that this series of earthquakes is following a similar pattern to 2001 and 2009 swarms in the same area in terms of magnitudes, frequencies and orientation along an axis running from northeast to southwest.

"There is nothing from past storms to indicate these were foreshocks to bigger events," but that possibility cannot be ruled out," Andrews said.

In 2009, the largest quake in the three-day swarm of about 450 events was a magnitude 4.8, she said.

The depths of the most recent quakes, while slightly deeper than in the earlier swarms, are still relatively shallow, meaning they will be more widely felt, Andrews said.

Additional quakes are expected over the next few days, she said.

The 4.8-magnitude quake on March 24, 2009 was the largest recorded event within 10 kilometers of today's swarm since records began in 1932.

City News Service; Photo: Shutterstock