Scientists are raising fresh concerns about the long-feared "Big One" after new geological research found that Southern California's major fault systems are now under the highest stress levels recorded in the last 1,000 years.
The findings, published in the Journal of Geophysical Research, suggest that the San Andreas and San Jacinto faults are simultaneously approaching stress conditions linked to some of the region's most destructive earthquakes.
Researchers from the University of Bern and an international team of geophysicists used a physics-based computer simulation to reconstruct earthquake activity dating back to 1100 AD. By combining radiocarbon dating, tree-ring analysis, historical rupture records, and fault stress modeling, the team tracked how tectonic pressure accumulated over centuries beneath Southern California.
Their results showed that stress levels along critical sections of the fault system have now exceeded anything seen in the simulation's millennium-long history.
"This simulation allows us to understand how stresses in the fault system build up over centuries," lead researcher Liliane Burkhard said in a statement. "The question of when and how the next major earthquake will occur in this region is one of the most pressing problems in applied geoscience."
Stress Levels Reach Historic Highs
According to the study, the San Jacinto-Bernardino fault section reached a stress level of 3.6 megapascals, while the southern San Andreas fault reached 2.8 megapascals.
Scientists say the concern is not only the magnitude of the stress itself, but the fact that both fault systems are highly stressed at the same time.
One megapascal equals approximately 145 pounds of force per square inch. Researchers explained that the pressure building beneath parts of Southern California is many times greater than the air pressure inside a standard vehicle tire.
The southern San Andreas fault has not experienced a major rupture in more than 150 years, increasing fears that energy has continued to accumulate beneath the region.
Cajon Pass Identified as an "Earthquake Gate"
The study identified the Cajon Pass area — where the San Andreas and San Jacinto faults converge near Interstate 15 — as a particularly dangerous zone, Futurism reported.
Researchers described the junction as an "earthquake gate," capable of determining whether a rupture remains confined to one fault or spreads across multiple fault systems simultaneously.
Historical earthquakes provide evidence of both scenarios. The devastating 1857 Fort Tejon earthquake, estimated at magnitude 7.9, remained primarily on the San Andreas fault. However, an earlier 1812 earthquake is believed to have propagated across both fault systems, causing a wider rupture.
Scientists warn that a similar multi-fault rupture today could have catastrophic consequences for Southern California.
Millions Could Be Impacted
The potentially affected areas include Los Angeles, San Bernardino, Riverside, and the Coachella Valley — regions that are home to millions of residents and host major transportation, rail, and energy infrastructure corridors.
Experts say a powerful earthquake crossing both fault systems could trigger widespread damage to roads, utilities, buildings, and communication networks throughout Southern California.
While modern seismic building codes and emergency preparedness have improved significantly since historic earthquakes like the deadly 1906 San Francisco earthquake, researchers caution that a major rupture could still overwhelm infrastructure and emergency response systems.
Scientists Stress There Is No Exact Prediction
Despite the alarming findings, researchers emphasized that the study does not predict a specific earthquake or timeline. Earthquake forecasting remains extremely difficult, even with advanced modeling tools.
Still, the research offers one of the clearest pictures yet of how stress is accumulating beneath Southern California and may help scientists better understand the conditions that precede major seismic events.
"Our results provide a clearer, physics-based picture of the current stress state of the fault system," Burkhard said. "The framework we developed is not just applicable to California, but also for other complex fault junctions worldwide."
© 2026 ScienceTimes.com All rights reserved. Do not reproduce without permission. The window to the world of Science Times.
