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More than 390 earthquakes triggered in California 'swarm'

August 27, 2012 |  2:46 pm

More than 390 earthquakes greater than magnitude 1 have hit Imperial County as part of a swarm that began Sunday, according to the U.S. Geological Survey.

A  magnitude 3.8 temblor hit at 10:02 a.m. Sunday about three miles northwest of Brawley, a 25,000-population city nestled between the San Andreas and Imperial faults.

The vast majority of the quakes measured under magnitude 3.0, but two topped 5.0, according to USGS data. A 5.3 temblor hit about 12:30 p.m. Sunday; a 5.5 quake followed about 90 minutes later.

PHOTOS: Earthquake swarm damages Imperial County buildings

The quakes continued Monday but at a slower pace. The total would be significantly larger if quakes below magnitude 1 are included.

Residents in Brawley were continuing to assess damage.

Brawley schools were closed Monday -- what was supposed to be the first day of the school year -- as inspectors surveyed the sites for damage. Imperial Valley College, about 10 miles south of Brawley, was open after an inspection Sunday showed no damage, according to the school's website.

Crews will have a better idea in the coming days of the total damage caused by the quakes, said Maria Peinado, a spokeswoman for the Imperial County Public Health Department; but so far the list of affected structures includes about 20 mobile homes shifted from their foundations.

The earthquakes also caused cosmetic damage to at least three buildings dating to the 1930s in downtown Brawley, said Capt. Jesse Zendejas of the city Fire Department.

A few displaced residents spent Sunday night at an American Red Cross shelter at the Imperial Valley College gymnasium, Peinado said. The shelter remained open Monday.

No major injuries have been reported, Peinado said, but officials were concerned that hot weather -- the National Weather Service predicted a high of 108 degrees Monday -- could cause problems for those cleaning up from the quakes.

Peinado said that although earthquakes weren't uncommon for the area -- aftershocks from a 7.2-magnitude Mexicali quake in 2010 rattled the region for days -- this swarm has been unsettling.

"It is a little disconcerting to have so many, even though they're little," she said.

The reason for the recurring swarms in the Brawley seismic zone is not fully understood. The most recent swarm was in 2005, when the area was shaken by hundreds of quakes, with the largest measuring magnitude 5.1, said USGS seismologist Rob Graves.

A previous swarm in 1981 recorded a top magnitude of 5.8, the highest on record in the area. Graves said the swarms can last for days but do not typically foreshadow a bigger quake in the Los Angeles area.

The succession of quakes rattled Brawley resident Alfonso Alvarez, who has a business renting bounce houses and other party supplies. Alvarez, 28, said he and his family had felt 15 quakes over 2 1/2 hours and, after the biggest one, had shifted to the frontyard.

“It’s been pretty bad. Some of them are slow and then they get intense,” he said. “We’re so anxious right now we can’t sit still.”


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