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Next great California quake is building up, say experts Roger Highfield / London Telegraph | June 22 2006 A century after a great earthquake killed thousands and made 300,000 homeless in San Francisco, a study of local geology shows that another is due in California. Today, a researcher investigating the stress building up at the San Andreas Fault using satellite data concludes that there is now sufficient energy for the next "big one" - an earthquake of magnitude seven or greater at the southern end of the fault, near Los Angeles and San Diego. The likelihood of a large earthquake may be increasing faster than researchers had believed, according to the study, led by Dr Yuri Fialko, of Scripps Institution of Oceanography at the University of California, San Diego, and published today in Nature. Although seismologists are not able to predict when a great earthquake will occur, most believe it is inevitable. Dr Fialko said his data suggested that "the fault is ready for the next big earthquake but exactly…when it will occur we cannot tell. It could be tomorrow or it could be 10 years or more from now." The Earth's surface is divided into several large tectonic plates separated by fault zones. The 800-mile San Andreas Fault divides the slow but steady movement of the North American plate, which moves south-easterly relative to the neighbouring Pacific plate. When plates slide past each other, which seismologists call "creep", strain accumulates less than when plates "lock" and stress loads continue to escalate, increasing the prospects of an eventual fault rupture and earthquake. But Dr Fialko found evidence that the southern San Andreas is mostly locked and continues to accumulate significant strain. He calculated the rate at which the fault is moving and estimated the "fault slip rate", the pace of the plate movement at the fault, at about an inch per year. During the last 300 dormant years the fault has accumulated approximately six to eight metres of slip "deficit". If released all at once, it would result in a magnitude eight earthquake, roughly the size of the 1906 San Francisco earthquake, he said. "We can say with some certainty that the fault is approaching the end of its loading period." The study also showed that the San Jacinto Fault, a lesser known branch fault that runs through populated areas in San Bernardino, Riverside and Borrego Springs is moving at twice the speed of previous estimates and is even more at risk of earthquake, probably at magnitude seven. ---------------------------------------------------
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