California Fault Capable of 8.0 Earthquake Begins Moving For First Time
By R.J. Johnson - @rickerthewriter
October 18, 2019
Residents in California have always known 'the Big One' could strike at any moment, wreaking havoc across the state, but, until a pair of powerful earthquakes struck near Ridgecrest in Southern California back in July, the ground had largely stayed quiet for the last 20 years. Now thanks to that shaking, scientists say a 160-mile-long fault that could generate an 8.0 quake has begun moving for the first time, a new study published in the journal Science on Thursday.
The Garlock Fault is located near the Mojave Desert in Southern California, just miles from where the rupture from the 7.1 quake (the strongest in California in more than 20 years), occurred. That quake helped trigger the Garlock Fault to begin moving, scientists say.
"The rupture of the main shock terminated only a few kilometers from the major regional Garlock fault, triggering shallow creep and a substantial earthquake swarm," the study said. "The repeated occurrence of multi-fault ruptures, as revealed by modern instrumentation and analysis techniques, poses a formidable challenge in quantifying regional seismic hazards."
"This is surprising, because we’ve never seen the Garlock fault do anything. Here, all of a sudden, it changed its behavior," the lead author of the study, Zachary Ross, assistant professor of geophysics at Caltech told the L.A. Times. “We don’t know what it means."
The Garlock Fault hasn't produced a large quake in nearly 500 years, according to Caltech scientists.
"We really have to remind ourselves that California is earthquake country," Ross said. "So, it's not just thinking about the largest, most damaging potential scenarios like events on the San Andreas, but remembering that there's a potential for hazard pretty much all over the place."
The study says that not only has the fault begun sliding for the first time in generations, it's also produced a swarm of small earthquakes in another section of the fault. The USGS said in September that the Ridgecrest quakes were not likely trigger a larger quake, however, officials cautioned that the 6.4 and 7.1 quakes back in July did raise the chances of an earthquake measuring magnitude 7.5 or above on one of the neighboring faults, which include the Garlock Fault.
A temblor on the Garlock fault could send strong shaking toward Los Angeles and its surrounding cities. Scientists say a quake on that fault could also place additional stress on the 300-mile long Southern San Andreas Fault, which could in turn, finally trigger the 'Big One' causing the worst quake in Southern California since 1857.
News of the sliding fault was published on the same day California released an earthquake early warning app and on the 30th anniversary of the deadly Loma Prieta quake along the San Andreas Fault. The California Earthquake Early Warning System (CEEWS) is an app people can download that alerts users if ground motion sensors installed across the state detect an earthquake. Depending on how far you are from the epicenter of the quake, the advance notice could give you anywhere from 10 to 30 seconds of advance warning that shaking is about to begin. The further away users are from the epicenter, the more time they'll have to find safety.
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