San Andreas, San Jacinto Faults Hit 1,000-Year Stress Highs as 3.6 MPa Builds Near LA
Updated
Updated · Gizmodo · Jun 9
San Andreas, San Jacinto Faults Hit 1,000-Year Stress Highs as 3.6 MPa Builds Near LA
3 articles · Updated · Gizmodo · Jun 9
Summary
New modeling shows Southern California’s San Andreas and San Jacinto faults have reached — and in places exceeded — their highest stress levels in the past 1,000 years, sharpening concern over a future major quake.
3.6 MPa of stress was estimated on the San Jacinto-Bernadino section, the highest in the simulation, while the neighboring Mojave South section of the San Andreas reached 2.8 MPa — a combination linked to larger cross-fault ruptures.
Cajon Pass, where the two fault systems meet northeast of Los Angeles, may act as an “earthquake gate” that determines whether a rupture stays on one fault or jumps both, raising potential consequences for nearby population centers.
The study reconstructed 1,000 years of earthquake cycles using 3D physics-based simulations fed by radiocarbon dating, tree-ring anomalies and historical rupture records.
Researchers said the findings do not predict when the next major earthquake will strike, but they point to a critically stressed fault system and support stronger hazard planning in Southern California and other complex fault zones.
With fault stress at a 1,000-year peak, is California's infrastructure truly ready for a joint megaquake?
How are new risk models changing insurance policies and emergency planning for millions of Californians?
Record-High Stress Levels at Cajon Pass Raise Urgent Joint Rupture Risk on San Andreas and San Jacinto Faults
Overview
A major study published in June 2026 used advanced earthquake cycle modeling and a reconstruction of 1,000 years of seismic history to reveal record-high stress levels on the San Andreas and San Jacinto faults, especially at their junction in Cajon Pass. This research provides a clearer, physics-based understanding of seismic hazards in Southern California and shows that Cajon Pass may pose a greater risk to nearby cities than previously thought. The findings highlight the importance of monitoring this complex fault system, as it could influence the likelihood and impact of future large earthquakes in the region and beyond.