A rash of moderate quakes shook the south end of the Salton Sea Sunday and early Monday. The largest of the quakes was felt from Orange County and San Diego County east into Arizona.
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"What we're seeing is a classic Brawley seismic swarm," USGS seismologist Lucy Jones told City News Service. "We haven't seen one of these since the 1970s, and there was another one back in the 1930s."
Some buildings were evacuated in Brawley, a small farm town 115 miles east-northeast of San Diego.
Small quakes were still being felt early Monday morning. A magnitude 2.4 quake occurred near the town at around 6:30 a.m.
"It's pretty bad. We had to evacuate the hotel just for safety," said Rowena Rapoza, office manager at the Best Western Hotel in Brawley.
Several structures in downtown Brawley were reportedly damaged. Isolated outages have been reported as well. The Imperial Irrigation District, which controls the power and water in Brawley, said it hopes to have the power restored later Sunday evening.
Heather Purvis, who lives in El Centro, told 10News the ground has been shaking all day.
"The first ones were at about 9 'o clock this morning," she said. "There was a little bit of a shaking, nothing major, but about 12:30 we felt about three different waves that were hard jolts
windows shaking, computer monitor falling off the desk. Those were a lot harder."
Jones said USGS seismographs and analysis computers were overwhelmed by the rash of rattling that began at sunrise, and reached a crescendo with a magnitude 5.3 quake just after 12:30 p.m. It was followed by a 4.9 shaker within two minutes.
"Our system is choking on so many earthquakes," Jones said. "This area of California is deep soils, and we do not get as precise data as we do over the rest of the state, and that makes our data a little less precise."
Preliminary computerized USGS reports had indicated that three quakes larger than magnitude 5.3 had rattled out from Brawley at 12:30. That was later resolved by seismologists to two quakes, magnitude 5.3 and 4.9, Jones told CNS.
Just before 2 p.m., a 5.4 magnitude quake was initially reported near Brawley. It was later upgraded to a 5.5 magnitude. Residents across San Diego County also reported feeling shaking. It was followed by lower magnitude quakes.
A 4.9 magnitude earthquake was reported by USGS at about 9:40 p.m.
The quakes were strongly felt at Borrego Springs, in San Diego County about 25 miles west of the epicenter.
"We've felt shaking for sure, but electricity has not gone out," said Gwenn Marie, owner of the Borrego Valley Inn.
The quakes were felt over all of San Diego County.
Fadi Atiya was looking at buying a penthouse on the 27th floor of the Sapphire Tower near Kettner Boulevard and A Street in downtown San Diego when the quake swarm hit.
"I was leaning up against the kitchen counter and I started swaying," he told 10News.
Atiya said at first he thought his legs were starting to give out because he had taken a 40-mile bike ride Sunday morning. A few minutes later, he realized it was not his legs, but Mother Nature.
Several miles east in the Valencia Park neighborhood, high school teacher Glenn Lee was putting on his shoes.
"I was sitting on the bed and I noticed that the bed moved," he said.
Like Atiya, he was not sure what was going on at first. A second later, things became clear.
"Another movement of the bed happened and it was a little bit sharper and right after that, my mom called me and she said, 'Hey, did you feel that earthquake?'" said Lee.
Lee added, "I went to the U.S. Geological Survey website and that's when I noticed that there were some big red marks and there had been a 5.3 earthquake."
There have been no reports of damage or injuries in San Diego County.
The quakes were also felt in Riverside and Imperial counties as well as Yuma and La Paz counties in Arizona, according to a USGS registry.
There was no damage reported in Riverside County, according to Melody Hendrickson, a spokeswoman for the Riverside County Fire Department. A dispatcher at the Riverside County Fire Department's Office of Emergency Services also reported no damage across the county.
Southern California Edison declared an "unusual event" as the quakes were felt in the control room of the San Onofre Nuclear Generating Station's twin reactors. Both of those nuclear piles have been in secure shutdown mode all summer, while federal and state officials work with the utility to discover why a recent upgrade and expansion caused parts of the boilers to shake violently. SC Edison said the notification was a standard step required by the federal government.
The ground about 5 miles north-northwest of Brawley began to spasm at sunrise, and Brawley was rocked by a magnitude 3.9 quake at 10:02 a.m., followed by a 3.4 quake about 90 seconds later.
In the three hours after the first earthquakes, an additional 11 quakes struck the same approximate epicenter near the Salton Sea. Quakes with magnitudes of 4.0, 4.0. 4.6 and 4.7 reportedly also hit during the noon hour.
The apparent quake cluster was centered 3 miles north-northwest of Brawley, 16 miles north of El Centro and about 115 miles east-northeast of San Diego. Some of the quakes may have been just east of Brawley.
Jones said the quake swarm was about midway between fault complex on the west side of the Imperial Valley, and the main branch of the San Andreas Fault, which runs from near Palm Springs to enter Mexico just west of Yuma.
"These don't seem to be related to earthquakes on the San Andreas itself, other than in a general way," she said. "It's pretty far away."
Jones says she expected the quake swarm "to continue to bubble along, they're going to get a bunch of 4s and 5s."
By midafternoon, the automated USGS lists were lengthy with reports of dozens of quakes echoing out from within 8 miles of Brawley. Jones has emphasized that many of the reported quakes are duplicates or have unreliable magnitudes, given the nature of the geology of the Brawley area.
As of 11:00 p.m. Sunday, there were 256 in or around Brawley. Forty of those earthquakes were magnitude 3.0 or higher.
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