San Andreas Fault Stress Reaches Highest Level in 1,000 Years, Study Finds

Researchers have published a study warning that stress accumulating on the San Andreas and San Jacinto fault systems in Southern California has reached its highest recorded levels in 1,000 years, and may exceed those levels in some segments. The study, led by the University of Hawaiʻi at Mānoa and co-authored by Liliane Burkhard of the University of Bern, modeled stress buildup and release using roughly 1,000 years of geological data, including radiocarbon-dated sediments and tree-ring records. The San Jacinto-Bernardino section alone has accumulated an estimated 3.6 megapascals of stress — equivalent to the pressure at 360 meters below the ocean surface — and a stress map shows peak Coulomb stress of approximately 3 MPa concentrated near Cajon Pass, east of Los Angeles. A particularly alarming finding is that Cajon Pass, where the two fault systems intersect, could under certain conditions act as an 'earthquake gate,' allowing both faults to rupture simultaneously in a single, far more destructive event affecting Los Angeles, San Bernardino, Riverside, and the Coachella Valley. The researchers stress that the study does not predict the timing of any earthquake, as that remains scientifically impossible, but argue the results should drive updates to infrastructure planning and building codes. The modeling methodology is designed to be generalizable and could be applied to complex fault intersections worldwide.