Southern California faults at highest stress in 1,000 years, study finds
Researchers report that Southern California's San Andreas and San Jacinto fault systems are now more stressed than at any point in the last 1,000 years, with the Cajon Pass junction northeast of Los Angeles critically loaded. A new study in the Journal of Geophysical Research: Solid Earth modeled 1,000 years of quake history and found stress on both faults high and similar, a configuration that has historically preceded ruptures crossing both systems. The team stresses this is not a prediction, but a sign the fault system is critically loaded.
A study led by the University of Bern, with the University of Hawaii, the U.S. Geological Survey, and Scripps Institution of Oceanography, modeled 1,000 years of earthquake history along the San Andreas and San Jacinto faults at Cajon Pass. Stress has reached, and in places passed, the highest levels in the period studied. The San Jacinto-Bernardino section is modeled at 3.6 MPa and the neighboring Mojave South section of the San Andreas at 2.8 MPa. When both faults run high and similar, conditions favor a rupture crossing the junction, as in 1812; the 1857 Fort Tejon quake instead stopped at the pass. Researchers say the findings matter for hazard assessment, infrastructure planning, and emergency preparedness. Source: Journal of Geophysical Research: Solid Earth (DOI 10.1029/2025JB033213).