New fault parallel to San Andreas Fault discovered - CBS News 8 - San Diego, CA News Station - KFMB Channel 8

New fault parallel to San Andreas Fault discovered

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SAN DIEGO (CNS) - A potentially significant fault that lies along the eastern edge of the Salton Sea has been discovered by scientists at the Scripps Institution of Oceanography at UC San Diego and the Nevada Seismological Laboratory at the University of Nevada Reno.

The so-called Salton Trough Fault runs parallel to the San Andreas Fault and could impact an earthquake-prone region that includes the greater Los Angeles area, according to the scientists' findings published in the October issue of the journal Bulletin of the Seismological Society of America.

The study's publication comes on the heels of a swarm of almost 200 small earthquakes that were detected in the Salton Sea area last week, shaking the nerves of Southern California residents who worried the temblors could be a precursor to a larger, more damaging and imminent quake on the southern San Andreas.

"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," said Scripps geologist Neal Driscoll, co- author and lead principal investigator of the study.

"We employed the marine seismic equipment to define the deformation patterns beneath the sea that constrained the location of the fault," he said.

Recent studies have revealed that the region has experienced magnitude-7 earthquakes roughly every 175 to 200 years for the last thousand years. A major rupture on the southern portion of the San Andreas Fault has not occurred in the last 300 years.

"We need further studies to better determine the location and character of this fault, as well as the hazard posed by this structure," said Valerie Sahakian, a Scripps alumna and lead author of the study.

"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," she said.

The research team used a suite of instruments, including multi-channel seismic data, ocean-bottom seismometers, and light detection and ranging, to map the deformation within various sediment layers in and around the sea's bottom.

"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," said Sahakian, a postdoctoral fellow at the U.S. Geological Survey's Earthquake Science Center.

The findings provide much-needed information on the intricate structure of earthquake faults beneath the sea and what role it may play in the earthquake cycle along the southern end of the San Andreas Fault, the researchers said.

Further research will help provide information about how the newly identified fault interacts with the southern San Andreas Fault. That could lead to more understanding of the more than 300-year period since the most recent large temblor.

"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 State Seismologist Graham Kent, a co-author of the study and former Scripps researcher.

"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," Kent said.

The study was funded by the National Science Foundation.

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