A study of how earthquake waves from the San Andreas fault travel through different types of Southern California soil marks what scientists say is a promising first step in an ambitious effort to pinpoint neighborhoods and even individual city blocks where the shaking would be most severe.
Researchers from the Southern California Earthquake Center hope to duplicate the research on hundreds of faults around the region, producing maps that show specific areas that face the greatest danger from the quake waves.
The scientists simulated two magnitude 7.7 temblors along the San Andreas fault to determine how the waves from the quakes would move across the region's topography.
They found that the waves from the San Andreas fault funneled northwest into the Los Angeles Basin, moving through the valleys that line the San Bernardino and San Gabriel mountains like water rushing through a trench.
The study identified several areas, including communities at the base of the San Gabriel Mountains, that would experience particularly strong shaking because the local topography would force waves toward the surface.
Researchers are entering data from hundreds of thousands of possible ruptures on other local faults and running computer simulations that map the direction and intensity of the waves.
They hope to have preliminary maps assessing the shaking risk in downtown Los Angeles, Pasadena and Long Beach in coming months.
Thomas Jordan, a USC geophysicist who runs the Southern California Earthquake Center, said the maps could eventually be used by city planners, insurance companies, real estate brokers and others to understand the quake risk of a particular piece of property.
But the prospect of detailed shaking hazard maps also raises questions about how much stock government, private industry and the public is willing to place in research that Jordan and others acknowledge, like most quake preparedness efforts, is speculative.
"We need to have a detailed discussion of how this information is going to be used and how society will respond to it," Jordan said.
This study was different from previous attempts to map the impact of a quake on the San Andreas fault because its authors applied the laws of physics to the waves and the Earth to get their results, said seismologist Ned Field, who studies earthquake hazards for the U.S. Geological Survey in Southern California.
