New research suggests stress along parts of Southern California’s San Andreas and San Jacinto fault systems has reached its highest level in at least 1,000 years.
The study, published June 3 in the Journal of Geophysical Research: Solid Earth, used computer models to study how earthquake stress has built up near the San Bernardino Mountains.
The findings do not mean a major earthquake is imminent. Scientists still cannot predict exactly when, where or how large the next earthquake will be.
Researchers focused on Cajon Pass, where the San Andreas and San Jacinto fault systems come close together.
The area may act like an “earthquake gate.” That means it can sometimes stop a rupture from moving between fault systems, or allow a larger rupture to continue through both.
A rupture involving both faults could affect densely populated areas, including Los Angeles, San Bernardino, Riverside and the Coachella Valley.
The research team used a physics-based model and fed it 1,000 years of earthquake history.
That history was reconstructed from evidence such as radiocarbon-dated sediments, tree-ring records and historical accounts.
The model found that stress normally released by major earthquakes has instead continued to build in key segments of the fault systems.
Seismologists say the study reinforces a long-standing concern: Southern California remains vulnerable to a major earthquake.
Ahmed Elbanna, director of the Statewide California Earthquake Center, told The Sacramento Bee that releasing the stress described in the study would likely require a magnitude 7 or larger earthquake.
But the timing remains unknown. The U.S. Geological Survey says neither USGS nor any other scientists can predict a major earthquake.
The study is a hazard warning, not a short-term prediction.
USGS says scientists can calculate the probability of a significant earthquake in a region over a period of years, but they cannot predict an exact date and time.
That distinction matters because alarming claims can spread quickly online after earthquake studies or smaller tremors.
California already has a statewide earthquake warning system that can give residents seconds of warning after a quake begins.
Earthquake Warning California, managed by Cal OES, uses ground sensors to detect shaking and send alerts through MyShake, Android Earthquake Alerts and Wireless Emergency Alerts.
Officials urge residents to prepare emergency supplies, secure heavy furniture and practice “Drop, Cover and Hold On.”
The study does not say Los Angeles will be hit tomorrow, next month or even next year.
It does say the region’s major faults are heavily loaded, and that a future rupture could be more complex if it crosses through Cajon Pass.
For millions of Southern Californians, the practical message is simple: the risk is real, the timing is unknown, and preparedness remains the best defense.