RELIVING THE ‘FRISCO QUAKE

Science  21 Apr 2006:
Vol. 312, Issue 5772, pp. 345d
DOI: 10.1126/science.312.5772.345d
CREDIT: COURTESY OF ARTHUR RODGERS

Scientists have created a series of simulations that describe in unprecedented detail the shaking and rippling of San Francisco during the massive earthquake that struck on 18 April 1906.

A consortium of government, industry, and university researchers started with a new U.S. Geological Survey (USGS) model of northern California that has geologic data on the nearby faults, including the San Andreas, extending as far as 45 kilometers below the surface. To digitally recreate the event, they added original seismic data, USGS ground measurements taken after the quake, and reports of shaking culled in the aftermath of the event.

Shawn Larsen, a seismologist and computer scientist at Lawrence Livermore National Laboratory who participated in the 2-year effort, says the simulation has yielded a new understanding of how seismic energy traveled east from the quake's epicenter just off the coast and shook California's central valley. Running hypothetical quakes of the same magnitude (roughly 7.8) with epicenters further north yielded terrifying results: “even stronger” ground shaking in San Francisco, Larsen says.

Previous models have given insights into other, smaller quakes, but this one required powerful machines like Livermore's 4000-processor Thunder supercomputer. David Wald of USGS, who was not part of Larsen's team, calls the simulation “the most comprehensive effort to date on this earthquake” and says it lays the groundwork for advances in mitigating future quake damage. The simulation was to be unveiled in San Francisco this week at a conference commemorating the 100th anniversary of the earthquake.

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