[Rockhounds] Desert quakes may have boosted chances of ‘big one’ striking California

[Kreigh Tomaszewski]

A pair of earthquakes that struck the remote California desert 1 year ago
have raised the risk of “the big one” hitting Southern California,
according to a new study. The research finds that the 2019 Ridgecrest,
California, quakes shifted underground stresses, making the San Andreas
fault—the state’s longest and most dangerous fault—three times more likely
to rupture.

“You would think an earthquake … out in the desert would have no impact on
Los Angeles,” says Ross Stein, a seismologist and one of the authors of the
new study. “But that is because we do not appreciate the way the network of
fault lines connect across the state.”

In July 2019, two faults near the town of Ridgecrest ruptured in quick
succession: a magnitude 6.4 on 4 July, followed by a substantial magnitude
7.1 a day and a half later. The temblors damaged buildings in the area, but
residents in Los Angeles, nearly 200 kilometers away, felt little more than
light shaking.

Yet the faraway earthquakes have raised the hazard for Los Angelenos, says
Stein, CEO of Temblor, a company that specializes in catastrophe modeling.
The reason, he explains, is that two quakes put new stresses on the Garlock
fault, a relatively dormant fault that runs through the desert toward the
San Andreas. The Garlock fault has not ruptured in 600 years, and given its
location in a sparsely populated region, it is not regarded as a great
threat. Yet, based on modeling from Stein and Shinji Toda, a seismologist
at Tohoku University, stresses resulting from the Ridgecrest quakes have
made the Garlock fault 100 times more likely to rupture—which would in turn
boost the chances of the San Andreas rupturing.

https://www.sciencemag.org/news/2020/07/desert-quakes-may-have-boosted-chances-big-one-striking-california