California is overdue for a major earthquake

California is tense, or at least its fault lines are. The southern part of the state is at risk of experiencing a devastating earthquake as stress levels along both the San Andreas and San Jacinto faults are at a peak. While researchers cannot predict when the earthquake will occur, understanding the state of these two fault lines and their associated risks can help to better prepare civilians and municipalities.

Tension at the gate

Stress levels along the San Andreas and San Jacinto fault lines have “now reached high levels,” and the “two fault systems may interact when their stress levels become similar,” leading to a massive earthquake, said a study published in the journal JGR: Solid Earth. After analyzing 1,000 years of paleoseismic data, researchers found that “stress along multiple portions of the faults is the highest it has been in at least a millennium,” said The Washington Post.

Earthquakes occur when a slip along a fault line “releases energy built up over time,” said CNN. Stress “accumulates as tectonic forces move the crust, but parts of the fault are locked and unable to slip freely.”

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While the Los Angeles area has seen its share of small earthquakes over the years, its last devastating quake was in 1857. The “violent magnitude-7.9 tremor ruptured a 225-mile stretch on the southern part of the San Andreas fault,” said the Post. Since then, that portion of the fault has “remained largely dormant, with stress continuing to build elsewhere along the fault, as well as along the neighboring San Jacinto fault.”

The two fault lines meet at a point called the Cajon Pass that could serve as an “earthquake gate.” A gate can “either stop or transmit large ruptures between the two faults,” said CNN.

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“The conditions that determine whether the earthquake gate at Cajon Pass opens or stays closed appear to be related to how closely the stress levels on the two fault systems are aligned with each other at the time of rupture,” said lead study author Liliane Burkhard in a news release. “Right now, with stress at historically high levels across the region and more than 160 years elapsed since the last major rupture, the system is in a critically loaded state.”

Magnitude prediction

Major earthquakes have occurred in other parts of California. There was a devastating 7.9-magnitude earthquake along the San Andreas fault in 1906 that affected San Francisco and the Bay Area. However, earthquakes in “one part of the fault network do not relieve pressure elsewhere,” said the BBC.

This research does not predict when the next giant earthquake will happen, but it does “improve our understanding of earthquake interactions in Southern California,” said the study. And knowing the risk can “help refine regional hazard assessments.”