The fault runs through populated areas including San Bernardino, Colton, Moreno Valley, Redlands, Loma Linda, Hemet and San Jacinto, as well as near Riverside, Rialto and Fontana. The epicenter of Friday’s quake was in a more isolated area near Borrego Springs.
Experts have been warning for some time that the San Jacinto fault – while less well known than the San Andreas – poses a major threat to the region.
A study released earlier this year said both faults could rupture together in a 7.5-magnitude earthquake.
"Because the San Jacinto fault cuts into the middle of the Inland Empire — instead of the edge of the desert — it cuts through a lot more people. There's just more people directly living on this fault," Julian Lozos, a Cal State Northridge professor of geophysics, who wrote the study while working on post-doctoral research at Stanford University and at the U.S. Geological Survey, told The Times in March.
That study looked at whether a massive 1812 quake in Southern California was the result of shaking on both fault lines.
The San Jacinto stretches for 130 miles, from the Cajon Pass in San Bernardino County southeast toward the Mexican border. The 1987 Superstition Hills earthquakes, which hit about 90 miles east of San Diego, topped out at magnitudes 6.5 and 6.7, and caused $3 million in damage in Imperial County.
According to the U.S. Geological Survey, a quake on the fault in 1918 caused significant damage and one death in San Jacinto.
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