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Earthquake swarm in Southern California appears to be slowing down

August 10, 2012 | 10:57 am

After two days, the swarm of earthquakes that rattled Southern California appears to be slowing down.

A series of more than 30 small to moderate temblors jolted the region beginning Tuesday night. Aftershocks continued into Wednesday and Thursday. But according to the U.S. Geological Survey's website, the last aftershock occurred at 1:11 p.m. Thursday. It was a magnitude 1.4 magnitude and likely was not felt by anyone.

The cluster of earthquakes in the vicinity of Yorba Linda was centered near the Whittier fault, but preliminary data suggest that the fault was not responsible for the all the shaking, said Doug Given, a USGS geophysicist.

"There are lots and lots of little faults all over that area," Given said of the northern Orange County region where the quakes were centered. "It's a known active area."

The shaking began with a magnitude 4.5 earthquake near Yorba Linda about 11:30 p.m. Tuesday, bookended by another 4.5 quake about 9:30 a.m. Wednesday, but with many smaller ones in between.

At a news conference Wednesday morning, Kate Hutton of the USGS said that of all the quakes, only three were probably felt by residents. The two 4.5 temblors were felt across a wide swath of Southern California, with people reporting shaking as far away as Thousand Oaks, the Santa Clarita Valley, the Westside and northern San Diego County.

"This is all part of the same earthquake sequence; they're all in the same area,'' Hutton told reporters. "We haven't had anything in the L.A. Basin in the last few years, but that doesn't mean we're totally quiet."

Given said the recent rumbling offers a lesson for the people in the region. "We live in earthquake country. Earthquakes are normal here, and people should be prepared," he said.


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