El Sol Market on Main Street in Brawley, Calif., was hit hard by the earthquakes… (Brandy Ronek, Associated…)
An "earthquake storm" continued to rattle Imperial County late Sunday, with the region experiencing hundreds of mostly low-intensity temblors that could be felt in neighboring counties.
The seismic activity is not unusual for the area around Brawley, a city of about 25,000 where the quakes were centered and located between the San Andreas and Imperial faults, experts said. The spurt of smaller quakes does not necessarily herald that the Big One is on its way, they said.
After a series of milder quakes in the morning, a magnitude 3.8 temblor hit at 10:02 a.m. about three miles northwest of Brawley, and was followed by a nearly continuous series of quakes in the same general area, according to the U.S. Geological Survey. The two largest quakes, which struck at about 12:30 p.m. and 2 p.m., measured at magnitudes of 5.3 and 5.5, respectively.
By 5 p.m., the USGS had recorded about 300 earthquakes, and the count continued to rise throughout the evening. The vast majority of the temblors measured under magnitude 3.0.
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 reached a 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.
"This type of activity has occurred in the past, and it has not preceded a large earthquake," he said, adding, "That doesn't mean it will always happen that way."
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 Imperial County Office of Emergency Services was working with the American Red Cross to set up a shelter at the Imperial Valley College gymnasium for families who were displaced after about 20 mobile homes shifted from their foundations.
The area saw scattered power outages, including at Pioneers Memorial Hospital. The hospital's generators kicked in, but officials decided to evacuate patients as a precautionary measure in case the building had suffered structural damage, said assistant hospital administrator Art Mejia. Hospital officials were inspecting the building with state regulators Sunday evening and had not seen evidence of such damage, he said.
The quakes rattled residents such as Alfonso Alvarez, who has a business renting bounce houses and other party supplies. Alvarez, 28, said he and his family had relocated to the front yard after feeling a series of 15 quakes in two and a half hours.
"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' "Did You Feel It?" system showed the quakes were felt as far away as San Diego, Temecula and San Clemente, including in the control room of the shuttered San Onofre nuclear plant. (There was no damage reported to the plant.) The 5.3 quake was also felt in Moreno Valley, Indio, National City and Palm Desert.