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Terrifying Multi-Fault Earthquake Could Strike Southern California

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A new study shows that the San Andreas and San Jacinto faults appear to have teamed up before

One of the side effects of living in the great state of California is the creeping sense of dread that comes with knowing that "the Big One" could strike at any time. Well, there's a new study in Science Advances that suggests that future earthquakes in Southern California could be even more damaging than previous models have suggested.

The study, written by Cal State Northridge professor Julian C. Lozos, finds historical precedent for earthquakes in which two fault lines rupture simultaneously.

In 1812, Southern California was struck with a major earthquake that devastated the mission at San Juan Capistrano. For years, seismological experts blamed a familiar suspect: the San Andreas Fault. Lozos, however, argues that the earthquake may have been the result of a joint effort between the San Andreas and San Jacinto faults.

Lacking modern-day seismic records of the quake, Lozos modeled the rupture using geologic evidence including the positioning of what the study refers to as "precariously balanced rocks." This modeling strongly suggested that the damage produced by the earthquake was the result of both faults working in tandem. According to Smithsonian, a separate study conducted by Cal State Long Beach geologist Nate Onderdonk indicates that multi-fault earthquakes have been occurring in California for thousands of years.

What does all this mean for SoCal? Most significantly, it suggests that many of our existing prediction models may be off. Most of the area's earthquake preparedness measures are based on the potential destruction caused by a single fault, yet a multi-fault rupture could cause greater devastation. The study also suggests that the San Jacinto Fault may be more of a hazard than previously assumed. This is bad news for the residents of San Bernardino and Riverside, the two closest major cities to where the San Andreas and San Jacinto faults intersect.