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Quakes still rattling Salton Sea area

March 26, 2009 |  8:20 am

Quakemap415

Earthquakes continued to rattle the Salton Sea area as a magnitude 4.0 quake rumbled through Wednesday at around 8:25 p.m.

More than 260 temblors have swarmed the area since Saturday, ranging from 0.4 to 4.8 in magnitude, said Caltech seismologist Kate Hutton. At least 12 of the quakes have measured 3.0 or above.

"We don't expect it to stop suddenly," Hutton said. "Most swarms go on for a week."

This is far from the largest swarm, she said, since some have thousands of earthquakes and last a couple of weeks. Seismologists have been keeping a close eye on the swarm because of the proximity of these quakes to the southern end of the San Andreas Fault.

So far, Hutton said, nothing appears unusual, and she has not heard about any earthquakes on the San Andreas itself.

"The risk is probably lower than it was after the 4.8, but it's not gone away," Hutton said. "Take it as a reminder to be ready for an earthquake at any time."

The swarms are one of the great mysteries of seismology in Southern California. Scientists have only recently begun to install more instruments to get a more detailed picture of what is happening.

"It's like someone flips a switch and it goes gangbusters, and then someone flips a switch and it turns off again," said Susan Hough, scientist in charge at the U.S. Geological Survey in Pasadena. "Exactly what's going on, I don't think we know."

-- Jia-Rui Chong

Photo: Image of Google map created by Broadband Seismic Data Collection Center (ANZA), Institute of Geophysics & Planetary Physics, Scripps Institution of Oceanography, UC San Diego Click here to visit the map (Editor's note: The map is not visible in Internet Explorer browsers; we recommend Firefox)

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