Scientist says Calif. is due for tremors

The famous fault line could lead to a major earthquake soon.
SCRIPPS HOWARD
Although he can't say just when, a scientist's new evaluation of slippage along the San Andreas fault suggests that the southern end of the major California seismic zone has reached levels of stress sufficient for a major earthquake.
The slippery meeting point of the Pacific and North American tectonic plates runs some 800 miles from the Salton Sea in the south to Cape Mendocino in the north. Historical records show there were massive earthquakes along the fault's central section in 1857 and along it's northern segment in 1906 (the San Francisco earthquake), but there has been no major rupture along the southern section of the fault for at least 300 years.
Numerous seismic experts have been warning for decades that a major earthquake of magnitude 7 or greater is inevitable along the 100-mile segment of the fault that cuts through Palm Springs, San Bernardino and Riverside, close enough to Los Angeles and San Diego to cause major damage.
The science
Yuri Fialko, an associate professor of geophysics at the Scripps Institute of Oceanography at the University of California-San Diego, used satellite images and other data about movement along the fault to come up with a new estimate of strain buildup along the segment that indicates the risk may be increasing faster than researchers have believed.
"For the public, the most important result of this study is that these data show definitively that the fault is a significant seismic hazard and is primed for another big earthquake," said Fialko, who published his findings today in the journal Nature.
"All these data suggest that the fault is ready for the next big earthquake, but exactly when the triggering will happen and when the earthquake will occur we cannot tell. It could be tomorrow or it could be 10 years or more from now," he added.
Seismologists know that the strain that accumulates as plates grind past each other is unequal. When the sliding is relatively steady and constant, which scientists call "creep," the stress load is less than when plates "lock" and the potential for an eventual fault rupture and earthquake increases.
Along with satellite images, Fialko combined data from geological records, GPS readings and seismic instruments to determine that the southern San Andreas is mostly locked and continues to accumulate significant amounts of strain.
He estimates the "fault slip rate" -- the pace of plate movement in the zone -- at about 1 inch a year. That means that during the past 300 dormant years, the fault has accumulated a slip deficit of roughly 19 to 26 feet.