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July 4th earthquake won't delay the Big One. And it might have worsened quake strain

Rong-Gong Lin Ii, Los Angeles Times on

Published in Science & Technology News

"Plate tectonics hasn't suddenly stopped; it is still pushing Los Angeles toward San Francisco at the same rate your fingers grow -- about 1.5 inches each year.... Their motion cannot be stopped any more than we could turn off the sun," Jones wrote in her recent book, "The Big Ones: How Natural Disasters Have Shaped Us (and What We Can Do About Them)."

The San Andreas is particularly feared because, in some sections, it will move for many feet almost instantaneously. A famous example was during the great 1906 magnitude 7.8 earthquake that destroyed San Francisco; at Point Reyes in Marin County, a fence that intersected the fault was suddenly cut in two, separated on each side by the San Andreas by 18 feet.

A similar sized earthquake of the San Andreas fault rupturing through the Palm Springs area would shatter the ground. If a couple had the misfortune of holding hands across the fault in a remote part of the desert near Desert Hot Springs when the Big One hits, they'd suddenly be separated by as much as 30 feet -- almost the entire length of a city bus, USGS research geophysicist Kate Scharer said in 2017.

Q: What about just the area that was hit by the Independence Day quake? Is that area now relieved of quake strain?

A: It actually probably made things worse for parts of some faults in that region, said earthquake scientists Ross Stein and Volkan Sevilgen, writing on their blog at Temblor.net.

The two wrote that they believe that parts of three other faults -- in remote areas of California -- were actually "brought closer to failure by the 4th July quake."

 

And in fact, they wrote, the area hit by Thursday's quake likely became loaded with more seismic strain after two previous temblors -- the 1872 Owens Valley and the 1992 Landers earthquakes.

Q: What has California's history told us about what moderate quakes can do?

A: Sometimes, a moderate quake -- after its series of aftershocks -- can lead to a period of seismic quiet. Other times, it can usher in a new era of temblors.

Q: What does an era of earthquakes look like?

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