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California Geological Survey

Probabilistic Seismic Hazards Mapping
Ground Motion Page

User Selected Site


Ground Motions for User Selected Site

Ground motions (10% probability of being exceeded in 50 years) are expressed as a fraction of the acceleration due to gravity (g). Three values of ground motion are shown, peak ground acceleration (Pga), spectral acceleration(Sa) at short (0.2 second) and moderately long (1.0 second) periods. Ground motion values are also modified by the local site soil conditions. Each ground motion value is shown for 3 different site conditions: firm rock (conditions on the boundary between site categories B and C as defined by the building code), soft rock (site category C) and alluvium (site category D).

Ground Motion Firm RockSoft RockAlluvium
Pga0.117 0.128 0.169 
Sa 0.2 sec0.27 0.295 0.393 
Sa 1.0 sec0.133 0.167 0.236 
NEHRP Soil Corrections were used to calculate Soft Rock and Alluvium.
Ground Motion values were interpolated from a grid (0.05 degree spacing)
of calculated values. Interpolated ground motion may not equal values
calculated for a specific site, therefore these values are not intended for
design or analysis.

Click here to return to the statewide PSHA map or enter new coordinates below:

Longitude: Latitude:

Please enter coordinates as Decimal Degrees
Example:   Longitude -122.0017   Latitude 36.9894

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Last edited on May 09, 2013
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