USA: California: July earthquake caused fault to move for first time on record

By Sam Levin

The large earthquake that hit southern California over the summer has increased strain on a major nearby fault, causing it to move for the first time on record, researchers said on Thursday.

Ruptures in the Ridgecrest earthquake sequence in July ended a few miles from the Garlock fault, which runs east-west for 185 miles (300km) from the San Andreas fault to Death Valley. That fault has been relatively quiet for 500 years, but now has begun slowly creeping, according to a new study released in the journal Science.

“It’s surprising,” Zachary Ross, assistant professor of geophysics at Caltech and lead author of the paper, said. “In California, we’ve been monitoring earthquakes for a long time. We think we have a pretty good sense of what typical behavior is over long timescales … and then when something happens that’s anomalous, that obviously stands out.

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The Ridgecrest earthquake sequence was the largest in two decades in southern California and began 4 July in the Mojave Desert about 120 miles (190km) north of Los Angeles. After a magnitude 6.4 foreshock, there was a magnitude 7.1 mainshock the next day, followed by more than 100,000 aftershocks.

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