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Seismic hazard mapping of California incorporating spatial variability of site conditions

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Abstract

The U.S. Geological Survey has recently released a 2008 version of the probabilistic National Seismic Hazard Maps. These maps plot the peak ground acceleration (PGA) and spectral acceleration (SA) ordinates at 0.2 and 1.0 sec with 2% and 10% probabilities of being exceeded in 50 years, corresponding to earthquake return periods of about 2,475 and 475 years, respectively. These acceleration levels were computed for uniform “firm rock” site conditions, i.e., 760 m/sec average shear-wave velocity in the upper 30 m, and therefore these maps do not show the potential spatial variability of ground motion associated with different site conditions, so we have combined the USGS National Seismic Hazard model with the California showing 17 generalized geologic units geologic units that can be defined by their shear-wave velocity (Wills and Clahan 2006), we regrouped these units into to 7 shear-wave velocities. At each shear-wave velocity value, a probabilistic seismic hazard map was generated for the entire state. By combining seismic hazard maps based on the 7 different shear-wave velocity values, a suite of seismic hazard maps was computed for California for 0.2 and 1.0 sec spectral ordinates at 2% probability of being exceeded in 50 years. The improved maps thus 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, which is intended to be accessible and understandable to the general public.

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Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Seismic hazard mapping of California incorporating spatial variability of site conditions
Year Published 2008
Language English
Publisher California Geological Survey
Contributing office(s) Earthquake Science Center
Description 8 p.
Larger Work Type Conference Paper
Larger Work Title Proceedings of the Third Conference on Earthquake Hazards in the Eastern San Francisco Bay Area : science, hazard, engineering and risk
Conference Title Third Conference on Earthquake Hazards in the Eastern San Francisco Bay Area
Conference Location Hayward, California
Conference Date October 22-24, 2008
Country United States
State California
Online Only (Y/N) N
Additional Online Files (Y/N) N