The Southern California earthquake swarm produced hundreds of temblors Sunday, and experts said it could last for several more days.
“Obviously, all this activity is related or interconnected, but it doesn’t really follow the typical main shock, aftershock activity,” said Rob Graves, a seismologist with the U.S. Geological survey.
Such earthquake storms are not unprecedented or unusual in that region. The most recent, Graves said, also centered near Brawley, was in 2005, when the area was shaken by hundreds of earthquakes, the largest measuring magnitude 5.1. A previous swarm in 1981 reached a magnitude of 5.8.
Seismologist Lucy Jones of the USGS said the region is known as the “Brawley Seismic Zone” and 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.
A number of families were displaced and hospital patients evacuated as a result of a swarm of hundreds of earthquakes earlier in the day.
No deaths or critical injuries were reported as a result of the quakes, the largest of which measured magnitudes 5.3 and 5.5.
Some buildings were damaged by the earlier quakes, including 20 mobile homes that shifted from their foundations, according to the Imperial County Office of Emergency Services. The office was working with the American Red Cross to set up a shelter for displaced families at the Imperial Valley College gymnasium.
The quakes cause scattered power outages, including at Pioneers Memorial Hospital, which lost power for about three hours. Assistant hospital administrator Art Mejia said generators immediately kicked in, but officials decided to evacuate patients as a precautionary measure in case the facility had suffered structural damage.
“We decided to err on the side of caution,” he said.
Patients in critical condition were transferred to other hospitals in the area or in San Diego and Riverside counties, while others were either discharged or moved across the street to a medical office building.
Mejia said Sunday evening that hospital staff and state regulators were walking through the hospital to assess the damages, but so far, the damages appeared superficial, including fallen ceiling tiles.
He said they hoped to be able to return patients to the hospital in a matter of hours.
Officials were urging residents to conserve water Sunday, and some schools were planning to close Monday, including Brawley Union High School, schools in the Brawley Elementary School District, Del Rio Community School and Mulberry Elementary.
County officials said updates would be posted on the Imperial County Emergency Medical Services Agency and the Imperial County Public Health Department‘s Facebook pages, and residents with questions about issues like school closures and water issues may call 760-351-2686.
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.”
source: LA Times August 27, 2012 – Local