The San Francisco Bay area is located in a broad zone of active crustal deformation driven by the motions of the North American and Pacific plates. Each year, about 5-6 cm (~2 inches) of relative plate motion must be accommodated in the Bay Area. During most years, at a given location only a small fraction of this motion occurs, and the rest is saved up, causing stress build-up. Geologic, geodetic, and geophysical studies show that plate motion is eventually released as slip along the San Andreas fault system, a complex group of sub-parallel faults (e.g., the San Gregorio-Hosgri, San Andreas, Hayward, Rodgers Creek, Concord, Green Valley, Calaveras, and numerous unnamed faults). Periodic seismic slip occurs when the stress build-up exceeds frictional resistance on these faults. Such slip can be dangerous and damaging as evidenced by the 1906 San Francisco and 1989 Loma Prieta earthquakes. The central California earthquake hazards project applies remote sensing techniques to study the subsurface and underwater geology of the San Francisco Bay area, where conventional geologic methods are impossible to apply.
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