Scientists rethinking threat posed by San Andreas
Written by
Gary Robbins
Jan. 26, 2012
The San Andreas fault is the dividing line between the Pacific and North American plates. It extends roughly 800 miles, from the Bombay Beach area of Southern California to the Bay area. USGS
The southern San Andreas fault -- a system large enough to produce highly damaging shaking in San Diego County -- appears to be shaped differently than scientists have long thought. The discovery, reported in the Bulletin of the Seismological Society of America, means that researchers will have to re-evaluate how the fault breaks and spreads energy.
The segment extends from the Salton Sea to Monterey County, a stretch that was believed to have a vertical dip in most areas. The new study says that sections of the fault are shaped more like a ship or airplane propellor.
"We haven't yet figured out why the fault does this, but probably, this shape makes it easier for the North American and Pacific Plates to move past each other," said Gary Fuis, a geophysicist at the US Geological Survey in Menlo Park.
The San Andreas divides the North American and Pacific, two of Earth's major tectonic plates.
"More research (and) modeling is needed to determine how and why it is easier to move the plates past each other with this propeller-shaped interface," Fuis said.
"One of the implications of this newly proposed fault geometry is that it will change the distribution of shaking that occurs when the fault ruptures in a big earthquake, such as the magnitude 7.8 Great ShakeOut Scenario earthquake that has been used for a few years in public drills," Fuis said.
The new study was conducted primarily by USGS and UCLA.
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