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Southern California earthquake points to danger of fault line

March 12, 2013 |  2:07 pm

 San Jacinto fault zone. Credit: USGS

This post has been corrected. See the note below.

Some might believe that the 4.7 magnitude Riverside County temblor that rattled windows and swayed skyscrapers across Southern California on Monday morning released tension from the San Jacinto fault, thereby avoiding danger of a larger earthquake.

But according to a study published in January in the journal Nature, conventional wisdom is wrong.

A pair of researchers, one from Caltech and the other from the Japan Agency for Marine-Earth Science and Technology, concluded that stick-slip faults similar to the San Jacinto fault that ruptured Monday aren’t limited to frequent, smaller temblors.

The authors pointed to the 2011 Fukushima earthquake in Japan. That quake, a 9.0, was born from a stick-slip fault that unexpectedly ruptured with devastating consequences.

Before that disaster, seismologists believed earthquake faults that experienced “creep,” or small, gradual movement throughout the year, had little chance of massive ruptures. The San Jacinto fault, Hutton said Tuesday, is one of those creeping faults.

“It does have frequent, small earthquakes but it does have big ones every now and then,” she said. “It doesn’t make it any safer.”

The San Jacinto fault is similar, with tectonic plates that slide horizontally against each other. Monday’s tremor was the biggest in three years and was felt across a wider swath than typical West Coast earthquakes, Susan Hough of the U.S. Geological Survey told the Los Angeles Times on Monday.

Scientists said the finding is forcing seismologists to rethink faults worldwide. A quake from San Francisco to San Diego along the San Andreas fault now seems more plausible, the study’s authors wrote.

For the Record, 3:52 p.m. March 12: An earlier version of this post incorrectly identified Susan Hough as Sarah Hough.


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-- Joseph Serna

Image: San Jacinto fault zone. Credit: USGS