A new study has found that tectonic stress on Southern California’s major fault systems has reached exceptionally high levels, raising important questions about future earthquake hazards in one of the most heavily populated regions of the United States. Researchers examined the San Andreas and San Jacinto fault systems and concluded that stress accumulation along parts of these faults is now greater than at any point during the last 1,000 years, with some segments potentially exceeding previous historical levels.
The research, led by scientists from the University of Hawai’i at Mānoa and published in the Journal of Geophysical Research: Solid Earth, focused on understanding how earthquake-related forces have built up and been released over long periods of time. To accomplish this, the team developed a sophisticated computer model that reconstructed approximately one millennium of earthquake activity. The model relied on geological evidence, including radiocarbon dating of displaced sediments and tree-ring records, which allowed researchers to estimate the timing and magnitude of past earthquakes.
Using these historical records, scientists simulated how tectonic stress has accumulated across the fault systems over centuries. Their findings indicate that the San Jacinto-Bernardino segment currently experiences stress levels of approximately 3.6 megapascals. While this value may appear modest on its own, researchers emphasize that the pressure acts across an enormous fault surface extending tens of kilometers horizontally and reaching depths of 10 to 20 kilometers beneath the Earth’s surface. Because the stress affects such a large volume of interconnected rock, a future rupture could release a tremendous amount of energy.
According to the study, the amount of energy released during an earthquake depends not only on the level of stress but also on the size of the fault area involved. When large sections of a fault remain locked for extended periods, tectonic stress continues to build. Eventually, if the fault gives way, the resulting earthquake can be significantly more powerful than smaller, more frequent seismic events that release stress gradually.
One of the most important areas examined in the study is Cajon Pass, where the San Andreas and San Jacinto fault systems intersect. Researchers describe this location as an “earthquake gate” because it can either prevent or permit seismic ruptures from transferring between the two fault systems. The study suggests that under certain conditions, a rupture could spread across both faults simultaneously. Such a combined event could generate a much larger earthquake than one involving only a single fault system.
A simultaneous rupture would pose substantial risks for Southern California communities, including Los Angeles, San Bernardino, Riverside, and the Coachella Valley, where millions of people live and work. The study indicates that tectonic stress has continued to accumulate in these fault systems for an unusually long period, potentially creating conditions for a significant future earthquake.
Despite these findings, the researchers stress that their work does not predict when an earthquake will occur. Current scientific methods cannot determine the exact timing of seismic events. Instead, the study provides valuable information that can improve earthquake hazard assessments, guide infrastructure investments, strengthen building codes, and enhance emergency preparedness planning. The researchers also note that their modelling approach could be applied to other complex fault networks around the world, offering a new tool for evaluating earthquake risks in regions where multiple fault systems interact.
https://www.euronews.com/2026/06/12/san-andreas-fault-reaches-highest-stress-level-in-1000-years