Study: multiple-fault ruptures can trigger stronger earthquakes

A new study by Stanford University could improve future seismic hazard predictions.

The new research reveals how the rupture of multiple faults can lead to stronger earthquakes. Based on the new findings, the 1812 earthquake of Southern California was likely due to the slippage of one fault triggering the rupture of a second fault.

Previously, scientists only blamed the San Andreas Fault for the 7.5 magnitude quake of Southern California. However, the study reveals the nearby San Jacinto Fault to be an accomplice.

The San Jacinto Fault has been underestimated in causing serious quakes in tandem with the San Andreas Fault.

“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,” said Julian Lozos, the author of the study published in ‘Science Advances’ and who is currently an assistant professor of geological sciences at California State University . “It’s important that we learn more about how activity on any single fault can affect other faults.”

This new study can improve future seismic hazard predictions. (Photo courtesy of :

This new study can improve future seismic hazard predictions.
(Photo courtesy of :

According to evidence found by the study, the San Jacinto Fault slipped first between the cities of San Jacinto and Moreno Valley. The rupture then travelled north and crossed over to the San Andreas Fault close to a place called the Cajon Pass. This location is where the two fault lines run as close as 1.5 kilometres. Together the two ruptured faults caused the Southern California earthquake on that ill-fated December morning.

“Understanding this earthquake in particular, and complex earthquakes in general, is important to quantifying seismic hazard”, said geophysicist Greg Beroza, the Wayne Loel Professor at Stanford School of Earth, Energy & Environmental Sciences.

Lozos’ research could help the Uniform California Earthquake Rupture Forecast (UCERF) in preparing for future earthquakes. In earlier UCERF reports the estimated chance of an earthquake shaking California by 2015 was about 4.7 percent. However, in its latest report, after taking into account the effect of multi-fault ruptures, this estimate has grown to about 7 percent.

Lozos also hopes his research increases earthquake awareness in the general public. Especially for the millions of Californians living in the Inland Empire, undercut by both the San Andreas and San Jacinto Fault lines.

“People shouldn’t just be thinking about the San Andreas Fault,” Lozos said. “There are lots of other faults, so it’s important for everyone in the regions at risk to have their earthquake kits ready.”

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