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Earthquake swarm 'classic' activity for Brawley area, USGS says

August 26, 2012 |  4:22 pm

Imperial County was hit by a swarm of earthquakes Sunday — including two measuring at magnitudes greater than 5.0 —  but experts said the activity doesn't mean "the Big One" was next.

The first quake — a magnitude 3.8 temblor — occurred at 10:02 a.m. about three miles northwest of Brawley, and was followed by a series of other quakes in the same general area, according to the U.S. Geological Survey. The agency's data have changed throughout the day, but the two largest quakes measured at magnitudes of 5.5 and 5.3.

Seismologist Lucy Jones of the USGS said the activity was not uncommon for the area, a region known as the "Brawley Seismic Zone" that sits between the San Andreas and Imperial faults. Similar swarms occurred in the area in the 1970s, she said, the most recent in 1981.

"This is a classic Brawley Seismic Zone swarm," she said. "It's relatively hot."

Experts can't predict what size temblors could come, but Jones said they have never seen a Brawley swarm produce anything larger than a magnitude 5.8 quake. That rattler was part of the 1981 swarm.

"We've never seen a Brawley swarm followed by a big earthquake on another fault," she added.

The current swarm could last for days, Jones said.

The earthquakes caused cosmetic damage to at least three buildings dating to the 1930s in downtown Brawley, said Capt. Jesse Zendejas of the Brawley Fire Department. Crews were still assessing other areas of the city, he said, but no injuries had been reported.

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 two and a half hours and, after the biggest one, had relocated to the front yard.

“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.”

The USGS' "Do You Feel It" system shows the quakes were felt as far away as  San Diego, Temecula and San Clemente. The 5.3 quake was also felt in Moreno Valley, Indio, National City and Palm Desert.

Lucy Navarro, who works at the front desk at the Vacation Inn in El Centro, said she felt two of the afternoon’s quakes, including the one that reached 5.3 magnitude at 12:30 p.m.

“The first one was pretty strong," she said. "That one scared me because it really shook me. I could see the building move."


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Image: Location of the epicenter. Credit: Google Maps