Southern California’s San Andreas and San Jacinto fault systems may be under their highest levels of tectonic stress in roughly 1,000 years, according to a new study that is drawing renewed attention to earthquake preparedness across the region.
The study, published in the Journal of Geophysical Research: Solid Earth, found that multiple fault segments in Southern California are now in what researchers described as a “critically loaded state.” Scientists said the findings suggest the region may be capable of a large rupture involving both fault systems, though the research does not predict when such an earthquake could happen.
The study was led by Liliane Burkhard, a research affiliate at the University of Hawaiʻi at Mānoa and scientist at the University of Bern. Her team used a physics-based model to examine how stress has built up and released along the faults over the past millennium.
The researchers focused heavily on Cajon Pass, a key junction where the San Andreas and San Jacinto fault systems come close together. That area may act like an “earthquake gate,” meaning it could either stop a rupture from moving between fault systems or allow a larger event to pass through and involve both systems.
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According to the study, the current alignment of stress between the two major fault systems is one reason scientists are paying close attention. If stress levels on both systems are closely aligned at the time of a rupture, Cajon Pass could be more likely to allow a larger, connected earthquake event.
Researchers used 1,000 years of reconstructed earthquake history to model present-day stress. That historical record included geological evidence such as radiocarbon dating, tree-ring data and documentation of past ground ruptures. The goal was to estimate how much stress is now stored in the system and how it compares with previous major events.
The findings do not mean a major earthquake is imminent. Earthquake scientists cannot predict the exact time, place or size of future earthquakes. Instead, the study offers a clearer picture of possible scenarios that emergency planners, infrastructure officials and residents should consider.
Southern California has long prepared for the possibility of a major earthquake, often referred to as “the big one.” The San Andreas fault is one of the most studied fault systems in the world, and the San Jacinto fault is also considered highly active. A large event involving both systems could affect densely populated areas, transportation corridors, water systems, power infrastructure and emergency response networks.
The last major destructive earthquake in the region was the 1994 Northridge earthquake, which struck the Los Angeles area before dawn and caused widespread damage. More than 60 people died, and tens of thousands of homes and businesses were damaged or destroyed. Although the Northridge quake did not occur on the San Andreas fault, it remains a reminder of how damaging Southern California earthquakes can be.
Scientists say the new study should be understood as a preparedness warning, not a prediction. A “critically loaded” fault system means stress has accumulated, but it does not provide a countdown clock. The main takeaway is that Southern California should continue strengthening buildings, updating emergency plans and educating residents about earthquake safety.
For residents, basic preparation still matters: securing heavy furniture, keeping emergency supplies, knowing how to shut off gas or water if needed, and having a family communication plan. For state and local officials, the research may support continued investment in seismic retrofits, transportation resilience and early-warning systems.
The study adds to a growing body of research showing that earthquake risk in California is complex. The danger is not only from one fault, but from how multiple systems interact. Cajon Pass may be especially important because it sits at a junction where one rupture could potentially connect to another.
That possibility does not guarantee a worst-case event. But it does suggest that emergency planning should account for multi-fault earthquake scenarios, especially in a region with millions of residents and major infrastructure built near active fault lines.
Why It Matters
The study matters because it suggests Southern California’s major fault systems are under unusually high stress compared with the past 1,000 years. That does not mean a major earthquake will happen immediately, but it does reinforce the need for serious preparedness.
A large rupture involving both the San Andreas and San Jacinto systems could have major consequences for transportation, housing, utilities and emergency response across Southern California.
What Comes Next
Researchers are expected to continue refining earthquake models to better understand how stress moves between fault segments and whether areas like Cajon Pass are likely to block or transmit ruptures.
For public officials, the findings may add urgency to earthquake readiness efforts, including building retrofits, public education, infrastructure planning and emergency response drills.
KTLA reported on the new study showing elevated stress levels along the San Andreas and San Jacinto fault systems in Southern California.
The San Andreas Fault and San Jacinto Fault Zone have reached their highest stress levels in 1,000 years, according to a study by researchers at the University of Hawaii at Manoa, leading scientists to wonder when California’s next “Big One” will occur. pic.twitter.com/fCoAQB5J1A
— KTLA (@KTLA) June 16, 2026
