In 2019, a pair of earthquakes hit the remote California desert that has raised the risk of "the big one" occurring in Southern California, a new study reveals. The research finds that last year's quakes shifted underground stresses, which caused the San Andreas Fault three times more likely to rupture.
"You would think an earthquake . . . out in the desert would have no impact on Los Angeles," says seismologist Ross Stein, 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."
California desert earthquake impact on 'the big one'
Two faults near Ridgecrest ruptured in quick sensation in July 2019. The first one was a magnitude 6.4 on July 4, then a day and a half later, followed by a 7.1 magnitude. Although earthquakes damaged buildings in the area, people in Los Angeles located nearly 200 kilometers away felt little more than light shaking of the Earth.
Temblor CEO Ross S. Stein said that despite the distance of the two places, the two quakes put new stresses on the Garlock fault, a dormant fault that extends through the desert towards San Andreas, which is why the faraway earthquakes raised hazard for the residents of LA.
For more than 600 years, the Garlock fault has not ruptured, and it was not regarded as a threat because it is located in a sparsely populated area. However, the models created by Stein and seismologist Shinji Toda at Tohoku University suggest that the two quakes have made the Garlock fault 100 times more likely to rupture, which raises the chances of the San Andreas of rupturing too.
According to the U.S. Geological Survey (USGS), the annual probability of an earthquake occurring in the San Andreas Fault is about one-third of 1% or, on average, that is expecting a magnitude 7.8 every 300 years.
However, the new model triples that possibility to 1% annually, which means that a big one could happen every century. If the Garlock fault would rupture, it raises further the potential of the big one to 50% in the following year.
What would happen if Garlock fault ruptures?
If ever a Garlock earthquake happens, it could lead to a rupture on the San Andreas for hours or days like the Ridgecrest earthquakes. USGS estimated 1,800 deaths and 50,000 injuries if a major San Andreas earthquake ruptures. There will be more than three million homes damaged and an estimated $289 billion reconstruction.
However, the value of the stress-transfer model used remains uncertain. It's the model used in predicting a 60% chance of a major earthquake within three decades following the 1999 Izmit earthquake in Turkey. So far, it has not happened yet.
On the other hand, another team published calculations after the 2004 Sumatran earthquake showing that it was likely to trigger a subsequent nearby rupture. A few days later, a massive event hit the island of Simeulue, just as foreseen.
Seismologist Morgan Page of the California Institute of Technology, who models quake risk for California, doubts that a large earthquake on the San Andreas may happen.
Amid all this anxiety, California deployed a system that can give digital warnings that outpace earthquake waves' speed. So, if a Garlock earthquake might happen, it would hit the Northern part of LA, in a perfect position for the warning system.
