David Perlman, San Francisco Chronicle Science Editor
San Francisco Chronicle March 11, 2011 04:34 PM Copyright San Francisco Chronicle. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.Saturday, March 12, 2011
(03-11) 17:34 PST SAN FRANCISCO -- Earthquakes the size of the one that struck Japan on Friday are highly unlikely ever to hit the California coast, but smaller quakes along the San Andreas or Hayward faults could prove just as devastating, experts say.
No temblor greater than a magnitude 8 is ever likely in California, say scientists at the U.S. Geological Survey in Menlo Park.
"But the next big quake in the Bay Area on either the San Andreas or the Hayward will be a $200 billion disaster," warned Thomas M. Brocher, who leads the USGS region's efforts at preparedness for the next Big One.
The San Andreas, which runs for some 810 miles from Cape Mendocino to the Salton Sea, is the state's most dangerous fault because the magnitude of any earthquake is primarily dependent on the length of a fault's rupture zone, explained Ross Stein, a geophysicist at the USGS.
But the north and south segments of the fault are separated by a central stretch of about 100 miles between Hollister and Parkfield in Monterey County, and it is that section that should prevent any earthquake as powerful as the one that struck Japan on Friday. In the Hollister-Parkfield segment, the brittle rock of the Earth's upper crust "is lubricated like talcum powder," Stein said. The result, he said, is a steady creeping motion that acts to relieve the constant buildup of stress within the fault that otherwise could trigger a major temblor along the entire length of the fault.
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