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Chance of big San Andreas earthquake increased by Ridgecrest temblors, study suggests

Rong-Gong Lin II, Los Angeles Times on

Published in News & Features

A new study suggests that last year's Ridgecrest earthquakes increased the chance of a large earthquake on California's San Andreas fault.

The study, published in the Bulletin of the Seismological Society of America on Monday, says there is now a 2.3% chance of an earthquake of magnitude 7.5 or greater in the next 12 months on a section of the 160-mile-long Garlock fault, which runs along the northern edge of the Mojave Desert.

That increased likelihood, in turn, would cause there to be a 1.15% chance of a large earthquake on the San Andreas fault in the next year.

Those odds may seem small. But they're a substantial jump from what the chances were before last year's Ridgecrest, California, earthquakes, whose epicenters were about 125 miles northeast of downtown L.A.

The new odds mean a large quake on the Garlock fault is now calculated to be 100 times more likely -- rising from 0.023% in the next year to 2.3%.

And the chance of a large quake on the San Andreas has roughly tripled, from 0.35% in the next year to 1.15%, said Ross Stein, a co-author of the study and the CEO of Temblor, a catastrophe modeling company in the Bay Area that has built a free earthquake hazards app for smartphones.


The Ridgecrest quakes could trigger a large quake on the Garlock fault, and that could trigger a quake on the San Andreas.

Seismologist Lucy Jones, who did not play a role in the report released Monday, called the study "elegant science" but added that its conclusions are not confirmed.

"It's really interesting science, and I like the way they've been able to increase the complexity of how they do their modeling. That's a real advance. But it's not yet proven," Jones said.

That said, Jones said that government officials in California should be prepared for a scenario in which an earthquake occurs that immediately raises the risk of a large quake on the San Andreas fault.


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