🌅 The San Andreas Fault Is “Critically” Stressed

SOURCE

Burkhard et al. (2026)

WHAT TO KNOW

• Researchers at the University of Hawaii built a computer model to simulate how tectonic stress builds up and releases along the San Andreas and San Jacinto fault systems in Southern California, finding the systems are at their highest levels of stress in the past 1,000 years. The study didn’t predict when either system would experience its next major earthquake, however, the researchers described the current state of stress as “critically loaded” and “unprecedented.”

WHY IT MATTERS

• Perhaps most importantly, the team found the two faults could rupture simultaneously, depending on what happens at Cajon Pass, where the San Jacinto fault splits from the main trace of the San Andreas fault. Cajon Pass acts as a “gate” that could either stop a quake in its tracks or allow it to propagate to the other system, depending on how similar the levels of stress are at the time of rupture. Unsurprisingly, the researchers found a joint rupture would be far more damaging than a single-fault event, putting densely populated areas like Los Angeles, San Bernardino, and the Coachella Valley at significant risk.

CONNECT THE DOTS

• Experts say that while the study has spawned countless headlines and indeed provides key scientific insights into the current state of stress on the two fault systems, broadly speaking, it really just reiterates what scientists and Southern Californians have known for some time: the region is overdue for a major quake. While definitions are regional, scientists in California typically consider quakes with a magnitude of around 8 or higher to be a “big one.” Southern California experienced its last big one in 1857, when a 217-mile-long segment of the San Andreas fault between Parkfield and Wrightwood slipped and caused a magnitude 7.9 quake. The rupture didn’t propagate through the Cajon Pass to the San Jacinto fault (i.e., the gate stayed “closed”), however, a 7.3 magnitude event that struck Wrightwood in 1812 did, suggesting it could happen again.