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Earthquakes Strike Southern California

Ben Schenk

Earthquakes Strike Southern California

CREATED Aug. 26, 2012

LOS ANGELES (CNS) - A rash of moderate quakes shook the south end of the
Salton Sea Sunday, 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.
   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.
   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.
   Southern California Edison reported 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.
   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.

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