CALIFORNIA: USGS Warns Bigger Quakes Could Strike

A swarm of small earthquakes hit desert communities near the Salton Sea Wednesday afternoon.

The biggest earthquake that has been recorded in the swarm so far was a magnitude 4.9, which hit at 5.31 p.m. local time on September 30, but bigger quakes are a possibility.

"In a typical week, there is approximately a three in 10,000 chance of a magnitude 7+ earthquake in the vicinity of this swarm,' the U.S. Geological Survey (USGS) said in a statement. "During this earthquake swarm, the probability of larger earthquakes in this region is significantly greater than usual. Currently, the swarm is rapidly evolving, and we expect to update this forecast with more specific probability information as we collect more data."

The quakes were centered near Westmorland in the Imperial Valley, just southeast of the Salton Sea. That's roughly 180-200 miles southeast of Los Angeles and about 30 miles north of the Mexico border.

By 8 p.m. the USGS had recorded at least 240 quakes, with the largest hitting a magnitude of 4.9 at 5:31 p.m.

Seismologist Lucy Jones said the quakes are happening in the Brawley Seismic Zone, a network of small faults that connect the San Andreas and Imperial faults.

Historically, she said, the largest quake in that zone measured 5.8.

She said the zone is a common source of swarms and far enough from the San Andreas fault so that a quake closer to the Los Angeles area is not any more likely.

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