The study outlines implications for seismic hazard assessments in one of the nation's most populated and infrastructure-critical regions.
Scientist Liliane Burkhard said that "the region may be capable of a large through-going rupture involving both fault systems," and that researchers "also found that Cajon Pass may act as an 'earthquake gate,' sometimes blocking large ruptures from crossing between the faults, and sometimes allowing them to pass through and involve both systems in a single event."
MORE: 2 major West Coast fault lines could be in sync and trigger double earthquake, scientists say
Looking back at 1,000 years of Earthquake History
Researchers designed a physics-based model that simulates the stress build up on the two fault systems including at the Cajon Pass.
By feeding the simulation 1,000 years worth of earthquake history from the region, they estimated how much stress has built up. Burkhard said, "Right now, with stress at historically high levels across the region and more than 160 years elapsed since the last major rupture, the system is in a critically loaded state."
The study found that stress normally released in large earthquakes has continued to grow up to unprecedented levels. It also found that the Cajon Pass could cause a joint rupture of both faults simultaneously. Densely populated areas including Los Angeles, San Bernardino, Riverside, and the Coachella Valley would be significantly affected.
The San Andreas Fault is the primary boundary between the Pacific and North American plates. It runs up the Peninsula and stretches about 650 miles, with other faults, including the Hayward Fault, branching off it.
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