Scientists are warning about hazardous fault lines in California, where tectonic pressure has reached its highest level in a thousand years. The findings of their study were published in the Journal of Geophysical Research: Solid Earth.
This event is referred to as the “California Big One” for good reason. Over more than a century, tectonic stress has been steadily and silently accumulating within the San Andreas Fault and the adjacent San Jacinto Fault.
A new computer model developed by researchers from the United States and Europe suggests that tectonic pressure in this region is “unusually high.”
“Our results indicate that stress levels at several points along the faults are currently at or above the highest values recorded over the last millennium,” says lead author Lillian Burkhard from the University of Bern in Switzerland. “Right now, with stress in the region at historically elevated levels and over 160 years having passed since the last major rupture, the system is in a critical state.”
Elevated pressure does not guarantee an earthquake in the near future, but it is causing concern among scientists like Burkhard.
The San Andreas and San Jacinto faults converge at the Cajon Pass, northeast of Los Angeles. Together, these two fault systems are responsible for 90 percent of the tectonic movement occurring between the North American and Pacific plates in Southern California.
This generates immense pressure, estimated at 2.8 MPa on the Mojave-South segment and 3.6 MPa on the San Jacinto-Bernardino segment. Over the past 160 years, both of these fault lines have remained ominously quiet. If the situation does not change, geophysicists fear a major earthquake is imminent, one that could cause severe damage to Southern California.
This includes densely populated areas such as Los Angeles County, Ventura County, Orange County, San Diego County, the Palm Springs-Indio metropolitan area, and even further south, down to Tijuana.
It is a disaster waiting to happen, but the exact timing remains the key question.
“This is not a prediction of when an earthquake will occur,” says Burkhard. “However, studies like this make a significant contribution to national and global seismic hazard research, as we apply rigorous quantitative methods to better understand the risk faced by millions of people.”
The point where the two faults meet is called the Cajon Pass, through which highways, railways, and energy corridors run, serving much of the Los Angeles metropolitan area.
Events occurring here, between the San Gabriel and San Bernardino mountains, could foreshadow the region’s future.
Scientists view this as an “earthquake gateway.” If it opens during a “shift,” it could affect both fault systems, triggering a larger and more complex catastrophe.
For further investigation, Burkhard and his colleagues teamed up with researchers from Northern Arizona University, the University of Bern, the U.S. Geological Survey, and the University of California, San Diego.
They developed a physics-based computer model to gain a deeper understanding of the fault history in the region and how the current situation came to be.
The international team of researchers fed their model with data on earthquakes over a thousand-year period in the area and then conducted simulations.
In some past earthquakes in the region, the “gateway” appeared to be closed, meaning ruptures stopped at the Cajon Pass and were confined to a single fault line. In other instances, it was open. When open, a joint rupture occurred, typically resulting in a larger and more complex earthquake.
“The conditions that determine whether the ‘earthquake gateway’ at the Cajon Pass will open or remain closed seem to be linked to how closely the stress levels in the two fault systems match each other at the time of rupture,” explains Burkhard.
Of course, these computer models are not a perfect representation of reality.
However, according to Burkhard, they help provide insights that could be crucial for risk assessment, infrastructure planning, and emergency preparedness.
At this point, that is essentially all we can do: gather as much information about the region as possible to be as prepared as we can be in the event of a fault rupture.
“One could say that the system is in a critical state, and that physics-based models like this one give us a clearer picture of the range of scenarios we need to be ready for,” Burkhard concludes.
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