The catastrophe modelling company Temblor have warned last year’s quakes have placed stress on the Garlock fault which links the Ridgecrest fault with the San Andreas fault. A rupture in the Garlock fault would trigger an earthquake north of Los Angeles.
Temblor CEO Ross Stein and Shinji Toda, of Tohoku University, said in a blog post: “In our study, we developed a new method to forecast future seismicity.
“These forecasts are not earthquake predictions, which have so far proven impossible.
“Rather, they are probabilistic, framed in the language of chance.
“We use past seismicity, the stress imparted by recent large and moderate earthquakes and the equations governing how fault friction varies in time and space (‘rate-state friction’) to estimate the likelihood of future earthquakes of different sizes.”
Scientists warn risk of San Andreas earthquake
California at risk of major earthquakes
During their analysis, their machine learning technology estimated a 2.3 percent chance of a magnitude-7.7 rupture within the next year.
The experts said: “This is 100 times higher than its annual chances in the ‘UCERF3’ benchmark model for California, which is jointly issued by the [US Geological Survey], the Southern California Earthquake Centre and the California Geological Survey.”
The researchers calculated if the Garlock fault was to rupture within 30 miles of its junction with the San Andreas Fault, it could “raise the probability of a San Andreas rupture extending to the southeast, on the so-called ‘Mojave section’, by a factor of about 150”.
They added: “That translates into a 50/50 chance of a San Andreas Mojave section rupture (with a range, 25 percent-67 percent), either immediately following a Garlock quake, or after some delay.”
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Ridgecrest earthquake last year cracked the ground
The likelihood of a large earthquake on the San Andreas has roughly tripled, from 0.35 percent in the next year to 1.15percent, said Mr Stein.
However, they said due to the small likelihood of the earthquake, the scientists say no one should panic.
They said: “But, as we have seen during the COVID-19 pandemic, low probability chain-reaction events do occur in nature, and when they do, their consequences can be great.
“It is the responsibility of scientists to assess the likelihood of such events, and then to bring them to the attention of the public and decision-makers.”
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Lucy Jones, a seismologist, praised the research study but said people in California should always be prepared for a possible earthquake.
She wrote on Twitter: “The chance of a San Andreas quake is up slightly, IF a Garlock quake happens because of Ridgecrest, and IF this model is correct.
“It’s elegant, but assumes a reason for quake triggering that is not consensus.
“The possibility of a San Andreas quake AT ANY TIME should already be part of your planning or you shouldn’t be in California.”
People in Ridgecrest examine the crack in ground
The report is the latest indication of a potential situation in which last summer’s quakes in a distant region of California might have began a succession of events that could provoke a large-scale earthquake on the San Andreas fault.
The San Andreas fault has not been seen in Southern California in 163 years.
At its nearest, the San Andreas fault appears within 35 miles of Los Angeles city centre.
Mr Stein added: “Now, you can think of the Ridgecrest earthquake as being so far from Greater Los Angeles that it is nearly harmless.
“But the problem is that the Ridgecrest earthquake brought the Garlock fault closer to rupture.
“If that fault ruptures — and it gets within about 25 miles of the San Andreas — then there’s a high likelihood, maybe a 50/50 shot, that it would immediately rupture on the San Andreas.”