Study Finds 1,000-Year Stress Highs at Cajon Pass — San Andreas Fault Lines
A new study found that stress along the san andreas fault lines has reached 1,000-year highs at Cajon Pass, about 50 miles from downtown Los Angeles. The junction sits where the San Andreas and San Jacinto fault systems meet, and the study says the site can shape how ruptures spread across Southern California.
Researchers described Cajon Pass as an earthquake gate and said the San Jacinto segment was the most heavily loaded portion of the junction. The study also found modeled stress levels of 2.8 on the Mojave South segment of the San Andreas Fault, 1.8 on the North San Bernardino segment, and 3.6 on the San Jacinto Bernardino segment.
Cajon Pass and San Jacinto
The study, published this month in the Journal of Geophysical Research, used computer simulations of the last 1,000 years of rupture history. It found that the San Andreas and San Jacinto fault systems may interact when their stress levels become equal, a condition that can affect whether one rupture stays on a single fault or moves across connected systems.
Over the past 1,000 years, the two fault systems have produced at least 36 earthquakes of magnitude 6.4 or greater. More than 100 years have passed since they produced a major earthquake, leaving the Cajon Pass junction as the part of the system researchers point to when they assess how strain could transfer between the faults.
Journal of Geophysical Research
The study adds a numerical benchmark to a junction already treated as critical because the Mojave South, North San Bernardino, and San Jacinto Bernardino segments all meet there. At 50 miles from downtown Los Angeles, that makes Cajon Pass the point where a future rupture could stay contained or spread across multiple connected fault systems.
The question for readers near Southern California is not whether the faults are active, but how the load at Cajon Pass may affect the path of the next major rupture. The study’s answer is narrower: the junction is already carrying stress at levels that match the highest modeled point in a millennium.
