Study Finds 1,000-Year Stress Highs at Cajon Pass San Andreas Fault Earthquake
A new san andreas fault earthquake study says stress has reached 1,000-year highs at Cajon Pass, the junction where the San Andreas and San Jacinto fault systems meet about 50 miles from downtown Los Angeles. Published this month in the Journal of Geophysical Research, the work ties that loading to a fault link that can either stop rupture or let it jump to another system.
The study used computer simulations to model the last 1,000 years of rupture history. It estimated stress levels 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, with the San Jacinto segment carrying the heaviest load at the Cajon Pass junction.
Cajon Pass Fault Junction
Researchers said Cajon Pass could act as an earthquake gate that significantly affects tectonic activity on nearby systems. The junction sits where the Mojave South and North San Bernardino segments of the San Andreas Fault meet the San Jacinto Bernardino segment of the San Jacinto Fault, giving a future rupture two possible paths through the same narrow connection.
That connection has a long record. Over the past 1,000 years, the San Andreas and San Jacinto fault systems produced at least 36 earthquakes of magnitude 6.4 or greater, and it has been more than 100 years since either fault produced a major earthquake.
Journal of Geophysical Research
The study’s timing gives the finding immediate relevance for people living and working near Southern California’s fault network. Cajon Pass is not an isolated line on a map; it is a junction where stress can accumulate across linked systems, and the model suggests that the strongest loading has built up where those systems meet.
The research does not point to a single rupture path. It says a future earthquake can sometimes halt at Cajon Pass and other times jump between the San Andreas and San Jacinto fault systems, which means the same junction could either limit spread or extend it across more of the region.
USGS 5.2 Earthquake
According to the USGS, a magnitude 5.2 earthquake was reported, and a Ring camera video showed shaking inside a San Diego home and a startled cat. The study sits alongside that recent shaking as a reminder that the region’s fault network is active even when the largest stress levels are being measured in the background.
For readers near the Cajon Pass corridor, the practical takeaway is simple: the junction is carrying stress at levels the study says match the highest seen in 1,000 years, and the fault systems on either side have a long history of large earthquakes. The next question is not whether the junction matters, but how much ground it can connect if a future rupture starts there.
