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Seismic Shaking
Hazard Maps of California
Seismic waves may be amplified by
near-surface materials. Loose or
soft soils typically amplify shaking
more than hard rock. The soils are
classified based on 1:250,000 scale
geologic maps (CGS's Geologic Atlas
Series Maps) and on shear wave
velocities measured in the upper 100
feet of the earth's surface at about
600 sites, primarily in the Los
Angeles and San Francisco Bay areas.
Shear wave velocity is used in
calculating the earthquake shaking.
Click on the image below to obtain a
more detailed version of the map.
 Soft
soils can amplify shaking and lead
to increased damage, as in the
Marina District of San Francisco
during the 1989 Loma Prieta
earthquake. Photo by J. Nakata,
USGS. |