Southern California's two largest fault systems are operating under unprecedented tectonic strain, reaching stress levels not seen in a millennium, according to a new study that has heightened concerns about the potential for a catastrophic earthquake.
Scientists at the University of Hawaii at Manoa analyzed 1,000 years of seismic history using computer models to assess current stress levels on the San Andreas and San Jacinto fault systems. Their findings, published in the Journal of Geophysical Research: Solid Earth, paint a sobering picture of a region in what researchers call a "critically loaded state."
"Stress levels on multiple fault segments are now at or above the highest values seen in the past millennium," said Liliane Burkhard, lead author of the research. "The region may be capable of a large through-going rupture involving both fault systems."
The epicenter of this concern lies at Cajon Pass, where the two faults converge. This junction acts as what scientists describe as an "earthquake gate" that can either block massive ruptures from spreading between the systems or allow both to rupture together in a single catastrophic event. More than 160 years have elapsed since the last major rupture in the region, during which stress has accumulated relentlessly.
"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," Burkhard explained. The alignment of these stress levels could be the difference between a localized quake and a region-wide disaster.
The research does not offer predictions about when such an event might occur, only that the physics-based models suggest the system is primed for significant seismic activity. "The system is critically stressed, and physics-based models like this one give us a clearer picture of the range of scenarios we should be prepared for," Burkhard said.
The study arrives at a time when California has long braced for what residents and officials call the "big one." The most recent major earthquake to devastate the state was the 1994 Northridge quake that struck just before dawn in the Los Angeles area. That disaster destroyed 87,000 homes and businesses and killed more than 60 people.
Author James Rodriguez: "This isn't speculation anymore - the math says Southern California is sitting on a pressure cooker at its historical limits, and the only question is when the lid blows."
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