Study Finds Stress on Southern California Fault Junction Reaches Millennial Highs
Computer simulations indicate that stress levels on fault segments near Cajon Pass have risen to values not seen in the past 1,000 years, raising the potential for a larger, multi-fault earthquake affecting the Los Angeles region.
A new study published in the Journal of Geophysical Research reports that tectonic stress along key segments of the San Andreas and San Jacinto fault systems near Cajon Pass has reached levels comparable to the highest estimates of the past millennium. The research used computer simulations of rupture history over the last 1,000 years to calculate stress values of 2.8 on the Mojave South segment, 1.8 on the North San Bernardino segment and 3.6 on the San Jacinto Bernardino segment, making the latter the most heavily loaded portion of the junction.
Cajon Pass, located about 50 miles northeast of downtown Los Angeles, is where the Mojave South and North San Bernardino sections of the San Andreas Fault intersect with the San Jacinto Bernardino segment. The authors describe the area as an "earthquake gate" that can either halt or transmit rupture between the two fault systems, potentially influencing the size and complexity of future earthquakes.
The study notes that the San Andreas and San Jacinto faults have produced at least 36 earthquakes of magnitude 6.4 or greater in the past 1,000 years, accounting for roughly 90% of the Pacific-North American plate slip rate in Southern California. Researchers caution that if a rupture were to propagate through Cajon Pass, it could spread to additional fault segments, increasing the likelihood of a larger, multi-segment event that would affect densely populated communities.
"The stress levels we have reconstructed suggest that Cajon Pass could play a pivotal role in determining whether a future earthquake remains confined to a single fault or cascades across multiple connected fault systems," the study authors said.