Cajon Pass and the Southern San Andreas Fault System: Earthquake Cycle Stress Accumulation and Present-Day Loading

With over a century since the last major rupture affecting the wider Los Angeles region, stress has been steadily building along the southern San Andreas and San Jacinto fault systems, raising concerns of an imminent large earthquake. The Cajon Pass, located at the junction of these faults, represents a critical site for potential through-going ruptures in Southern California. We constructed new 4D earthquake cycle simulations using a 1000-year paleoseismic rupture history of the San Andreas Fault System (SAFS) to assess spatial and temporal variations in stress thresholds. A semi-analytic Fourier transform model was used to compute stress from 3D dislocations in an elastic plate overlying a Maxwell viscoelastic half-space, assuming complete coseismic stress drop. Results show highest stress accumulation north of Cajon Pass (~1.8 MPa/100 yrs) due to greater slip rates, and lower rates south of the Pass (~1.0-1.5 MPa/100 yrs). By 2025, Coulomb stress is estimated at 2.8 MPa on the Mojave South (MOS) segment, 1.8 MPa on the North San Bernardino (NSB1) segment and 3.6 MPa on the San Jacinto Bernardino (SJB) segment. Each segment accumulates stresses within characteristic threshold ranges: 1.2-2.7 MPa for MOS, 0.4-1.6 MPa for NSB1, and 1.2-2.9 MPa for SJB. When the stress disparity between segments SJB and MOS narrows, the faults appear to rupture jointly, suggesting Cajon Pass may act as an earthquake gate. These results inform seismic hazard assessments by linking stress evolution to fault interaction potential. Information & Authors Information Version history Copyright This work is licensed under a Non Exclusive No Reuse License.

Authors Metrics & Citations Metrics Article Usage 372views 222downloads Citations Download citation Liliane ML Burkhard, Bridget Renee Smith-Konter, Katherine M. Scharer, et al. Cajon Pass and the Southern San Andreas Fault System: Earthquake Cycle Stress Accumulation and Present-Day Loading. Authorea. 27 October 2025. DOI: https://doi.org/10.22541/au.176159502.27356408/v1 DOI: https://doi.org/10.22541/au.176159502.27356408/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu.