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Multi-Fault Ruptures Can Trigger Larger Earthquakes, Stanford Study Finds

SAN FRANCISCO (CBS SF) -- One of the strongest earthquakes in California history was likely caused when one fault line slipped and triggered another slippage along the San Andreas fault, according to new research.

The 7.5 magnitude Wrightwood earthquake in San Bernardino County killed 40 Native Americans inside Mission San Juan Capistrano when the structure collapsed on them on December 8, 1812.

Up to now, researchers had attributed a slip along the San Andreas fault for the earthquake.

According to a study by Stanford scientists, the much lesser-known San Jacinto fault provoked the movement on the San Andreas fault, leading to a more powerful temblor.

RELATED: Magnitude 3.5 Quake Hits NorCal

"This study shows that the San Jacinto fault is an important player that can influence what the San Andreas fault is doing and lead to major earthquakes," study author Julian Lozos, told the Stanford News Service. "It's important that we learn more about how activity on any single fault can affect other faults."

The research would likely help in preparing future versions of the Uniform California Earthquake Rupture Forecast (UCERF), which provides estimates of the magnitude, location and likelihood of large earthquakes.

California Fault Model Evolution Until UCERF3 Release by SCEC on YouTube

The latest UCERF data estimates the chance of a magnitude 8 or larger earthquake to hit California by 2045 rose to seven percent from about 4.7 percent in a previous forecast.

UCERF data also indicates the San Francisco Bay Area has a greater risk of large earthquakes because two fault lines, the Calaveras and Hayward-Rogers faults, have not had a large earthquake in a long time.

COMPLETE QUAKE COVERAGE: CBS Earthquake Resource Center

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Carlos E. Castañeda is Senior Editor, News & Social Media for CBS San Francisco and a San Francisco native. You can follow him on Twitter or send him an email.


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