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A Major Earthquake Fault in California Just Woke Up

Garlock Fault showing activity for first time in modern history after this summer's tremors
By John Johnson,  Newser Staff
Posted Oct 18, 2019 10:19 AM CDT

(Newser) – You've heard of the San Andreas Fault. Meet the smaller, lesser-known Garlock Fault, also in California. It hasn't gotten many headlines over the years because the Garlock has been essentially sleeping for the past 500 years or so. But after the summer's two major quakes in and around Ridgecrest, things have changed. In Science, researchers say the Garlock has begun moving for the first time on record. Alarming news? Not necessarily, but scientists are tuned in, given the theoretical chance that a major tremor on the Garlock could set off an even more destructive quake on the San Andreas. Details:

  • The creep: The bigger of the Ridgecrest quakes, one that measured 7.1 on July 5, ended just a few miles from the Garlock Fault. Satellite radar now shows that the Garlock has begun to "creep" for the first time on record. "This is surprising, because we've never seen the Garlock Fault do anything," Zachary Ross of Caltech, lead author of the study, tells the Los Angeles Times. "Here, all of a sudden, it changed its behavior. We don't know what it means."

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  • The fault: The Garlock measures about 185 miles, and it runs from the San Andreas Fault to Death Valley, per KTLA. It's on the northern edge of the Mojave Desert. A major Garlock quake—and scientists say the Garlock is capable of producing one of 8.0 magnitude—would affect the San Fernando Valley, farming and oil-producing regions, major state aqueducts and routes, even Edwards Air Force Base. But another fear is that a Garlock quake could trigger a major tremor on the southern San Andreas Fault, which would have devastating effects in Los Angeles and elsewhere in Southern California.
  • Perspective: The chances of that doomsday scenario happening are small, per the Times. And creeping faults don't necessarily translate to big quakes, as evidenced so far by the San Andreas. The newspaper, however, adds that the study "punctuates a persistent myth"—that quakes such as this summer's reduce the chance of future quakes. "In fact, earthquakes make future earthquakes more likely."
  • Dominoes: Another takeaway from the study is that risk zones aren't confined to major fault lines, notes CBS Los Angeles. The Ridgecrest quakes, for example, were caused by 20 small, intersecting faults. Each on its own might not have been able to set off a big earthquake, but together they were trouble. "You can think of this as one fault triggering another like dominoes," say Ross. "That really shows us that even if there is not a really large fault somewhere, you can still have significant seismic hazard."
  • New app: The study came out Thursday, the same day California released an earthquake early warning app, notes USA Today. The app's release was timed to mark the 30th anniversary of the 6.9 Loma Prieta earthquake along the San Andreas Fault.
(Read more earthquake stories.)

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