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California earthquake swarm: 19 homes red-tagged; temblors continue

August 30, 2012 |  9:09 am

PHOTOS: Earthquake swarm damages Imperial County buildings

Imperial County declared a local emergency on Wednesday as officials tallied damage from the swarm of earthquakes that continued Thursday.

There were more quakes overnight, but they were significantly smaller than the ones felt on Sunday when the swarm began.

The Imperial County Board of Supervisors declared the emergency after getting more information about damage. According to the Imperial Valley Press, 19 mobile homes have been red-tagged, several buildings -- including a school auditorium -- have been closed because of damage and water pipes broke. There has been no total damage estimate.

PHOTOS: Earthquake swarm damages Imperial County buildings

More than 400 earthquakes greater than magnitude 1.0 have been recorded in Imperial County since Saturday evening, said U.S. Geological Survey geophysicist Elizabeth Cochran. The largest were a 5.3 and a 5.5 about midday Sunday.

Scientists say the reason is not fully understood, but there is a clue: Earthquake faults work much differently south of the Salton Sea than they do closer to Los Angeles.

Take, for instance, the San Andreas fault as it runs through Los Angeles County. It’s a fault where, generally speaking, two plates of the Earth’s crust are grinding past each other. The Pacific plate is moving to the northwest, while the North American plate is pushing to the southeast.

South of the Salton Sea, the fault dynamic changes. The Pacific and North American plates start to pull away from each other, Cochran told The Times from her Pasadena office. (That movement is what created the Gulf of California, which separates Baja California from the rest of Mexico.)

So Imperial County is caught between these two types of faults in what is called the Brawley Seismic Zone, which can lead to an earthquake swarm, Cochran said.

The  last major swarm was in 2005, Cochran said, when the largest magnitude was a 5.1. The largest swarm before last weekend's occurred in 1981, when the biggest quake topped out at 5.8. Before that, there were swarms in the 1960s and 1970s.
Crews will have a better idea of the total damage caused by the quakes in the coming days, 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 Brawley Fire Department.

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


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Photo: Vanessa Ledon reacts to a mess inside the storage room of the 24 Seven market in Brawley after several small earthquakes hit Sunday. Credit: Fernando Acosta Jr. / Imperial Valley Press