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In southern
California, there is significant seismic hazard from a major earthquake
on the San Andreas fault. The southern part of the fault has not
seen a major event since 1690, and the accumulated slip may amount
to as much as six meters, setting the stage for an earthquake that
could be as large as magnitude 7.7. But scientists and engineers
wanted to know in more detail just how intensely the earth will
shake during such an event—and what impact this will have
on structures, particularly in the populated sediment-filled basins
of Southern California and northern Mexico.
Members of the
SCEC/CME collaboration including 33 earthquake scientists, computer
scientists, and others from eight institutions have produced the
largest and most detailed simulations yet of just what may happen
during a major earthquake on the southern San Andreas fault.
The TeraShake
simulations modeled the earth shaking that would rattle Southern
California if a 230 kilometer section of the San Andreas fault ruptured
producing a magnitude 7.7 earthquake. Two rupture scenarios were
simulated, one rupturing from north to south, beginning near Wrightwood,
California, and a second one rupturing from south to north, starting
near Bombay Beach, California.
The geographic
region for the simulations was a large rectangular volume or box
600 km by 300 km by 80 km deep, spanning Southern California from
the Ventura Basin, Tehachapi, and the southern San Joaquin Valley
in the north, to Los Angeles, San Diego, out to Catalina Island,
and down to the Mexican cities of Mexicali, Tijuana, and Ensenada
in the south.
To model this
region, the simulations used a 3,000 by 1,500 by 400 mesh, dividing
the volume into 1.8 billion cubes with a spatial resolution of 200
meters on a side, and with a maximum frequency of .5 hertz—the
biggest and most detailed simulation of this region to date. In
such a large simulation, a key challenge was to handle the enormous
range of length scales, which extends from 200 meters—especially
important near the ground surface and rupturing fault—to hundreds
of kilometers across the entire domain.
The results
and resources produced by these simulations are summarized on this
site. Please let us know your thoughts and comments.
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