Seismic Hazard Mapping of California Considering Site Effects

Earthquake Spectra, Nov., 2010

Erol Kalkan, U.S. Geological Survey, Menlo Park,
Chris J. Wills, California Geological Survey,
Dave M. Branum, California Geological Survey,

Plain English Summary

U.S. Geological Survey has released a 2008 version of the National Seismic Hazard Maps. These maps plot the peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2 and 1.0 sec with 2% and 10% probability of exceedance (PE) in 50 years. These acceleration levels were computed for uniform “firm rock” site conditions (VS30 = 760 m/sec), and therefore the potential spatial variability of ground motion associated with different site conditions are not considered. In this paper, we have combined the National Seismic Hazard model with the California geologic map showing 17 generalized geologic units that can be defined by their VS30. We regrouped these units into 7 VS30 values and calculated a probabilistic seismic hazard map for the entire state for each VS30 value. By merging seismic hazard maps based on the 7 different VS30 values, a suite of seismic hazard maps was computed for 0.2 and 1.0 sec spectral ordinates at 2% PE in 50 years. The improved hazards maps explicitly incorporate the site effects and their spatial variability on ground motion estimates. The SA at 1.0 sec map of seismic shaking potential for California has been now published as California Geological Survey Map Sheet 48.

California Seismic Hazard

California Seismic Hazard Map Considering Site Effects (VS30) | Download KML Files

California State-wide VS30 Map (showing geological variations)| Download KMZ File

Printable ArticleCGS Map Sheet 48Press Friendly California Eq. Potential Map

Printable article (5 Mb) | CGS Map Sheet 48 (37 Kb) | High Resolution California Seismic Hazard Map (Media Version) (10.5 Mb)

High Resolution California Seismic Hazard Map for 0.2 s (9.9 Mb) | 1.0 s (8.9 Mb)


Downloadable Gridded Spectral Values (ASCII Format) For VS30 = 160, 216, 287, 377, 489, 609, 760 m/s
2% PE in 50 years………………..……….. PGA | SA(0.2) | SA(1.0)

Earthquake shaking potential (SA = 1.0 s) for California considering spatial variation of local geological conditions


Earthquake shaking potential (SA = 1.0 s) for San Francisco and Los Angeles metropolitans considering local site effects