Cajon Pass Reaches 1,000-Year Stress Peak, Modeled as Rupture Gate on San Andreas-San Jacinto System

Researchers led by Liliane Burkhard at the University of Bern built a physics-based model that tracks stress transfer across three fault dimensions and time, incorporating paleoseismic, tree-ring, and historical data. The simulation reproduces known ruptures and calculates how each event alters neighboring segments while interseismic loading and post-seismic relaxation continue. Output places current stress at or above the model maximum across multiple Cajon Pass segments. The junction functions as a conditional gate: depending on local stress orientation it can arrest or permit rupture transfer between the San Andreas and San Jacinto faults, as seen in the 1857 stop and 1812 through-going events. Stress accumulation since 1857 has now surpassed the threshold that previously allowed passage. Public-safety implications center on the greater Los Angeles basin, where a multi-fault rupture would increase ground-motion severity and damage extent. The model does not forecast timing but indicates the mechanical conditions for a larger event are now at their highest in the millennium-long record. Next steps require integration of real-time geodetic data and updated paleoseismic trenches to test whether the simulated stress field matches present-day measurements.