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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.

Preliminary Surface Geologic Materials (Soils)

Click on the image below to obtain a more detailed version of the map.

Preliminary Surface Geologic Materials

Marina District damage, Loma Prieta Earthquake, San FranciscoSoft 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.


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