New Calif. Fault Line Found: 'Salton Trough' Parallels San Andreas

With the October 2016 earthquake swarm and southern California residents on edge prepping their earthquake kits and developing family action plans, a publication by the Scripps Institute of Oceonography at University of California, San Diego and the Nevada Seismological Laboratory at the University of Nevada Reno announced a big discovery this week.

The group announced a brand new fault line, what it has named the "Salton Trough." This newly discovered fault line lies along the eastern edge of the geologically active Salton Sea and runs parallel to the San Andreas Fault.

What does this mean?

A fault line in this location could theoretically impact the earthquake-prone region of 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.

With a recent swarm of 200 small earthquakes that were detected in the Salton Sea area the last week of September, Southern California residents are watchful of more damaging and imminent quakes along 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.

Further Study Needed

"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.

What role will the Salton Trough play in future earthquake structure mapping?

"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.

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 be conducted on how the newly identified fault interacts with the southern San Andreas Fault. That will create a deeper understanding of the 300-year-plus period since the most recent large temblor in Southern California.

"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.

City News Service contributed to this report. Image, USGS Web site screenshot