Scientists discover second major fault line near San Andreas

A newfound fault running parallel to the San Andreas Fault could help explain the nearly 200 small earthquakes experienced by southern California residents last week, according to a study appearing in the Oct. 16 edition of the Bulletin of the Seismological Society of America.

First detected by scientists from the University of California, San Diego’s Scripps Institution of Oceanography and the Nevada Seismological Laboratory at the University of Nevada, Reno, the fault lies along the eastern edge of the Salton Sea, a shallow salt-water lake located directly over the San Andreas Fault and predominantly in California’s Imperial and Coachella Valleys.

The discovery of what has been dubbed the Salton Trough Fault raises some concerns that a larger earthquake on the southern San Andreas Fault could be forthcoming, and could drastically impact current seismic hazard models in the quake-prone region that includes Los Angeles and the surrounding area, the researchers said Tuesday in a statement.

The “potentially significant” new fault was discovered using a number of different instruments, including multi-channel seismic data, ocean-bottom seismometers, and LIDAR (light detection and ranging) equipment, the study authors added. Using this technology, the study authors were able to map deformations in sediment layers in and around the seafloor. The newfound fault is a strike-slip fault located just to the west of the San Andreas one, they explained.

Will California See Another Huge Earthquake?

Mapping earthquakes can play a key role in preventing fatalities and limiting damage during a seismic event, the research team explained. As lead author Valerie Sahakian noted, “To aid in accurately assessing seismic hazard and reducing risk in a tectonically active region, it is crucial to correctly identify and locate faults before earthquakes happen.”

“The location of the fault in the eastern Salton Sea has made imaging it difficult and there is no associated small seismic events, which is why the fault was not detected earlier,” added Scripps geologist and study co-author Neal Driscoll. “We employed marine seismic equipment to define the deformation patterns beneath the sea that constrained the location of the fault.”

The new report comes in the wake of other recent studies which discovered the region had experienced magnitude-7 earthquakes at least once every 200 years over the past 1,000 years, the researchers said. No major ruptures have occurred in the southern part of the San Andreas Fault in more than three centuries, however. Further analysis of the new fault could help explain why this has been the case by determining how it interacts with its infamous counterpart.


The San Andreas Fault. (Credit: US Geological Survey)

“The extended nature of time since the most recent earthquake on the Southern San Andreas has been puzzling to the earth sciences community,” said Nevada seismologist Graham Kent. “Based on the deformation patterns, this new fault has accommodated some of the strain from the larger San Andreas system, so without having a record of past earthquakes from this new fault, it’s really difficult to determine whether this fault interacts with the southern San Andreas Fault at depth or in time.”

“We need further studies to better determine the location and character of this fault, as well as the hazard posed by this structure,” added Sahakian. “The patterns of deformation beneath the sea suggest that the newly identified fault has been long-lived and it is important to understand its relationship to the other fault systems in this geologically complicated region.”


Image credit: UC San Diego