Balancing boulders suggest San Andreas fault may shake less than once feared

SAN FRANCISCO— Someday, a great earthquake will erupt from the San Andreas fault, which cuts through Southern California from Los Angeles to San Francisco. Geologic records make it clear. It has happened, and it will happen again . But when the Big One does hit, it may be less devastating than once thought, at least near Los Angeles. According to new work presented this week at a meeting of the American Geophysical Union, the ground there will shake up to 65% less violently than official hazard models suggest. The good news for Angelenos stems from five rocks balanced precariously on top of other rocks in Lovejoy Buttes, a place in northern Los Angeles County that sits just 15 kilometers from the fault. By dating when the rocks first became fragile and analyzing their structures to assess the maximum shaking they could withstand, the researchers could test official predictions against thousands of years of earthquakes. Those predictions have been found wanting, says Anna Rood, a seismic hazard scientist at the Global Earthquake Model Foundation who led the work, which is accepted in Seismological Research Letters . “The hazard estimates are totally inconsistent with these precariously balanced rock data.” The new study is a welcome advance for an emerging technique, says Daniel Trugman, a seismologist at the University of Nevada, Reno. “They’ve applied probably the most rigorous methodology that I’ve ever seen t...
Source: ScienceNOW - Category: Science Source Type: news