Diverting the Colorado River took a load off the faults that run underneath California, literally.
In the past, the Salton Sea in Southern California periodically flooded, which may have caused small “stepover” faults beneath the Sea to trigger the much larger San Andreas Fault.
The smaller faults run perpendicular to the San Andreas Fault, and when then rupture, they can have a domino effect on the San Andreas causing it to unleash massive quakes. The first domino in the line may have been the flooding of the Salton Sea in the past. But a study published recently in Nature Geoscience suggests human use of the water may have removed that domino.
BLOG: How the Mississippi River Triggers Earthquakes
"We've been baffled as to why the Southern San Andreas hasn't gone. It's been compared to a woman who is 15 months pregnant," said Scripps seismologist Debi Kilb, a report co-author, in a University of California in San Diego press release. "Now this paper offers one explanation why."
The stepover faults under the Salton Sea were recently discovered by researchers at Scripps Institution of Oceanography, the University of California in San Diego, the U.S. Geological Survey (USGS) and the University of Nevada in Reno.
NEWS: Haiti Quake Caused by Previously Unknown Fault
"To fully understand the hazards and rupture scenarios associated with the southern San Andreas Fault, we can't limit our study to the San Andreas Fault itself," said Danny Brothers, a grad student at Scripps when he conducted much of this research, but now with the USGS, in a University of California in San Diego press release.
"These stepover zones really need to be considered when assessing earthquake hazards and need to be examined as potential triggers for destructive earthquakes on the larger faults."
The Salton Sea used to collect the waters from the Colorado to fill Lake Cahuilla. But since the early 1900s, much of the Colorado has been diverted to irrigate farms. The result was a much smaller body of water, only 1/25th the size of Lake Cahuilla.
The San Andreas used to let loose with a massive quake every 180 years or so, but for the past 300 years, the fault has refrained from releasing the whole of its destructive power. The San Francisco quake of 1906 was the work of the northern section of the San Andreas, but the southern portion remains a major threat to Los Angeles.
"Earthquake simulations reveal that shaking of large metropolitan areas such as Riverside and Los Angeles will be larger if the earthquake propagates from south to north - our research suggests that the Salton Sea stepover zone may provide a trigger for such a propagation direction," said Scripps geologist Neal Driscoll, a report co-author.
Recently conservation efforts have been underway to restore the Salton Sea ecosystem. Besides the danger to Los Angeles and other human population centers, a quake could threaten restoration efforts.
"Large earthquakes on the southern San Andreas most likely will be accompanied by liquefaction in the Imperial Valley. In addition to ground shaking, the liquefaction will cause damage to water conveyance systems and existing infrastructure in the region and is likely to affect Salton Sea restoration efforts," Brothers said.
A quake caused by by the southern San Andreas could occur without a trigger from Salton Sea flooding. Tectonic forces, or the movements of the Earth's plates, are capable of triggering a quake without the influence of Salton Sea flooding. Other researchers estimate that the energy building up in the fault could produce a quake between magnitude 7 and 8.
Other areas where bodies of water and seismic faults coincide may be able to learn from this research.
BLOG: China Quakes Give US Temblors Pause
"Not only were we able to address seismic hazards issues along the San Andreas Fault, but this research also highlights the broader use and capabilities of new techniques and technologies to study hazards under bodies of water," said Graham Kent, director of the Nevada Seismological Laboratory at the University of Nevada, Reno and a co-author of the report.
"This can have application for other regions where the presence of water has left problems undetected," said Kent.
The research also shows how much is still unknown about the extent to which humans are influencing Earth systems.
IMAGE 1: Abandoned, salt-encrusted structures on the east shore of the shrinking Salton Sea (Wikimedia Commons).
IMAGE 2: This map shows the current Salton Sea boundaries and outline of Lake Cahuilla at its peak size as well as locations of major area faults (USGS).
IMAGE 3: The Salton Sea in 2007 (Wikimedia Commons).
Tags: Conservation, Floods, Natural Disasters, Plate Tectonics, Rivers
comments ( )