A new study raises new concerns about earthquake risk in Southern California. Researchers say the region’s two major fault systems – the San Andreas Fault and the San Jacinto Fault – are experiencing more cumulative stress than at any time in the past 1,000 years. The findings do not predict when earthquakes will strike, but suggest conditions now are similar to those before some of the region’s largest historical earthquakes. The research was published in Journal of Geophysical Research: Solid Earth Led by Dr. Liliane Burkhard of the University of Bern, Switzerland.
Pressures beneath major faults hit record highs
Earthquakes occur when stress slowly builds up along a fault and is suddenly released. To understand how much pressure is currently stored beneath Southern California, Dr. Liliane Burkhard and her team used 1,000 years of earthquake records to create a physics-based model. The researchers relied on geological evidence, including radiocarbon dating, tree-ring records and past earthquake data.
The results are stunning. According to the study, stress levels in parts of both fault systems have reached or exceeded levels seen over the past millennium.
One section of the San Jacinto Fault records the highest stress levels found anywhere in the model, while nearby sections of the San Andreas Fault show similarly high values. The researchers said the combination left the region “severely loaded.”
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Cajon Pass may affect Southern California earthquake risk
A major focus of the study is Cajon Pass, a mountain pass northeast of Los Angeles where the San Andreas and San Jacinto faults are in close proximity. Scientists describe the area as an “earthquake gate” because it stops a rupture from spreading and also allows it to jump from one fault to another.
The study found that both fault systems now experience highly matched stress levels. In the past, similar situations have been associated with earthquakes that spanned multiple faults rather than rupturing on just one.
If this happens again, earthquakes could affect densely populated areas including Los Angeles, San Bernardino, Riverside and the Coachella Valley. The researchers noted that this scenario could be more damaging than an earthquake limited to a single fault.
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The researchers stress that their work is not a prediction and does not provide a date for future earthquakes. Instead, they say the findings paint a clearer picture of the current situation and can help emergency planners, engineers and officials prepare for potential risks in the future.
