Did You Feel It? 5.5 Quake Shakes Brawley

The temblor is part of another cluster of quakes, this time emanating from the Imperial Valley. It included at least six quakes of 4.0.

A series of small earthquakes expanded into a rash of moderate quakes at the south end of the Salton Sea today, and the largest quakes were felt from Orange County and San Diego east into Arizona.

"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. "It's pretty bad, we had to evacuate the hotel just for safety," said Rowena Rapoza, office manager at the Best Western Hotel there.

Southern California Edison reported that both of its units at the San Onofre Nuclear Generating Station were offline at the time of the earthquakes and did not experience any damage. In compliance with regulations, it filed a second Notice of Unusual Event after a quake was felt in the control room at 2:03 p.m.

Jones said USGS seismographs and analysis computers were overwhelmed by the rash of rattling that began at sunrise, and reached an apparent crescendo with a magnitude 5.3 quake just after 12:30 p.m. It was followed by a 4.9 shaker within two minutes, but a 5.5 quake followed more than an hour later, at 1:57 p.m.

"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.

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, Riverside and Imperial counties, and in Yuma and La Paz counties in Arizona, according to a USGS registry.

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 were also 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."

—City News Service

GreenInOC August 27, 2012 at 02:21 PM
In LN, I felt two of them sometime around 11am and another between Noon and 1pm. Heard them before I felt them. Both lasted a while but were fairly gentle and didn't inspire a response.
Martin Henderson August 27, 2012 at 03:43 PM
The second part of the quote is impressive, too: Seismic swarm. As a writer, I wish I'd have thought of that.
jim August 27, 2012 at 04:22 PM
The swarm contained more than 50 distinct earthquakes of magnitude 3.0 and above, 2 of which were above 5.0. if you count them all, there were over 300 above a magnitude of 1.0. If you are interested in watching a live earthquake map, see: http://earthquake.usgs.gov/earthquakes/map/
Donna Gilmore August 27, 2012 at 06:23 PM
Felt one of them in San Clemente mid day and another smaller one last night. My first concern was "is San Onofre safe?" Even with the plant shut down, there are tons of highly toxic radioactive waste being stored there, much of which must have electricity in order to keep it continuously cooled with ocean water so it doesn't melt down. The CPUC has approved new earthquake studies that ratepayers are being required to pay 100%. They obviously think it's unknown how safe San Onofre is so they're spending $64 million of our money for these studies and related activities. The USGS says no one has ever predicted a major earthquake, so what's the point of the studies? Also, the seismic studies will include sonic tests that will seriously harm sea mammals and other marine life. Fukushima had a 9.0 earthquake near it, so maybe the plant should be designed for this worst case? Money would be better spent to protect the toxic waste pools from earthquakes rather than on more studies. http://sanonofresafety.org/earthquake-and-tsunami-risks/
ms.sc. August 27, 2012 at 07:32 PM
The Ring-of-Fire. I watch that on my homepage daily. That is why SONGS is/ was a bad idea. I actually am not in favor of anything nuclear.


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