By KiddieDaily Editors · Jul 2, 2026 · 3 min read · Ages 10–12 · 1 source

Earthquake Researchers Discover Dangerous Stress Levels Building Beneath Southern California

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Scientists modeled a millennium of earthquake history and found unusually high stress accumulating along major Southern California faults.

For more than 150 years, Southern California’s most powerful faults have been storing energy deep underground. While the region experiences frequent small earthquakes, geologists know that the largest and most damaging events are separated by long periods of relative quiet as tectonic stress steadily accumulates. Much of that stress is concentrated along the San Andreas and San Jacinto faults, two major fault systems that accommodate the movement between the Pacific and North American tectonic plates.

Northeast of Los Angeles, the faults converge near Cajon Pass, a geologically complex junction that has long intrigued scientists because a rupture on one fault could potentially spread onto the other. The last major earthquake to impact the broader Los Angeles region was the magnitude 7.9 Fort Tejon earthquake in 1857. Since then, stress has continued to build along these fault segments, creating an unusually long quiet period that researchers have increasingly viewed as a cause for concern.

Liliane Burkhard of the Division of Space Research and Planetary Sciences (WP) at the Physics Institute of the University of Bern modeled a millennium of earthquake activity along the southern San Andreas and San Jacinto fault systems to estimate how much stress is now loaded at Cajon Pass. The international team included researchers from the University of Hawaiʻi at Mānoa, the U.S. Geological Survey Earthquake Science Center in Pasadena, and the Scripps Institution of Oceanography at UC San Diego.

The findings indicate that tectonic stress in the area has reached, and in some places surpassed, the highest levels seen in the past 1,000 years. The study also describes Cajon Pass as an “earthquake gate”: a fault junction that helps determine whether a large earthquake stays on one fault or spreads across both systems at once. The study has just been published in the Journal of Geophysical Research: Solid Earth.

To examine how stress has changed over time along the San Andreas and San Jacinto faults and at the key Cajon Pass junction, the research team built a physics-based earthquake cycle model in four dimensions, meaning it simulates three spatial dimensions as well as time. The model was then supplied with a 1,000-year earthquake record reconstructed from geological clues, including radiocarbon dating, tree ring anomalies, and historical records of ground ruptures. “The model tracks how each earthquake changes stress on neighboring fault segments, how stress accumulates during the quiet intervals between events, and how the deeper layers of the crust slowly relax following large ruptures,” explains Burkhard.

“This simulation allows us to understand how stresses in the fault system build up over centuries,” continues Burkhard. “By running the earthquake history of Southern California as a simulation, we can estimate the extent to which the fault system is already under stress today.”

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