Flooding of Ancient Salton Sea Linked to San Andreas Earthquakes — The West Ranch Beacon

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(From Science Daily) Southern California’s Salton Sea, once a large natural lake fed by the Colorado River, may play an important role in the earthquake cycle of the southern San Andreas Fault and may have triggered large earthquakes in the past. Researchers at Scripps Institution of Oceanography, UC San Diego, the U.S. Geological Survey (USGS) and the University of Nevada, Reno, discovered new faults in the Salton Sea near the southern end of the San Andreas Fault. By examining displacement indicators preserved in pristine sedimentary deposits, the team reconstructed their earthquake history and found evidence for coincident timing between flooding of the ancient Salton Sea and fault rupture. Rupture on these newly discovered “stepover” faults has the potential to trigger large earthquakes on the southern San Andreas Fault.

The report appears in the online version of the journal Nature Geoscience on June 26.

The Salton Sea covers a structural boundary at the southern end of the San Andreas Fault where it takes a southwestward step to the Imperial Fault. The region is closely monitored because the last large earthquake on this section of the San Andreas occurred approximately 300 years ago and the fault is considered by many experts to be overdue for another.

By imaging beneath the Salton Sea, the study identified the key role of stepover faults that run at an angle to the San Andreas Fault. The smaller faults rupture relatively frequently and, at times, they ruptured in concert with Colorado River flooding of the Salton Trough. Report lead author Danny Brothers said that this research does not improve the ability to predict such a quake but suggests that heightened preparedness for a major quake immediately following smaller quakes in the stepover zone is warranted.