Researchers find San Andreas Fault stress at 1,000-year high
Liliane Burkhard said the san andreas fault system is in a critically loaded state after more than 160 years since the last major rupture. A University of Hawaiʻi at Mānoa-led study found tectonic stress along Southern California’s San Andreas and San Jacinto fault systems has reached, and in some areas exceeded, the highest levels seen in the past 1,000 years.
The study, published in the Journal of Geophysical Research: Solid Earth, says the region is not showing signs of an imminent rupture. It does say the system is under unusually high stress in a long-term seismic cycle and could support large earthquakes, including multi-fault events.
Cajon Pass and linked ruptures
One focus of the research is Cajon Pass, the junction between the San Andreas and San Jacinto fault systems. Researchers described it as an earthquake gate that may block ruptures from crossing between faults or allow them to link into a single larger event.
Burkhard, a research affiliate at the University of Hawaiʻi’s Institute of Geophysics and Planetology and a scientist at the University of Bern, said, "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". Researchers said that load is not a signal of immediate rupture, but it does place the fault network in a condition where a larger event becomes more plausible over time.
Southern California fault network
Researchers said a rupture involving both fault systems could be significantly more damaging than a single-fault earthquake. They named Los Angeles, San Bernardino, Riverside, and the Coachella Valley as major population centers that could be affected by a larger rupture.
The San Andreas Fault is a strike-slip plate boundary where the Pacific Plate and North American Plate slide past each other horizontally. During a major rupture, parts of California can shift suddenly by feet or even tens of feet, while most earthquakes do not produce surface rupture.
The study leaves readers with a narrow but practical takeaway: the fault system is carrying record stress, but researchers are not pointing to an imminent break. For people in the region, the immediate implication is not a timed warning but a stronger case for treating a multi-fault earthquake as a real possibility in the state’s largest population corridors.
