In this paper, we have combined the U.S. Geological Survey's National Seismic Hazard Maps model with the California geologic map showing 17 generalized geologic units that can be defined by their VS30. We regrouped these units into seven 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 seven different VS30 values, a suite of seismic hazard maps was computed for 0.2 and 1.0 s spectral ordinates at 2% probability of exceedance (PE) in 50 years. The improved hazards maps explicitly incorporate the site effects and their spatial variability on ground motion estimates. The spectral acceleration (SA) at 1.0 s map of seismic shaking potential for California has now been published as California Geological Survey Map Sheet 48.
We update annualized and scenario earthquake loss estimations for California using HAZUS, a loss estimation tool developed by the Federal Emergency Management Agency, and evaluate the effects of changes in input ground motions over the last decade on estimated earthquake losses. Our estimated statewide average earthquake loss to building stock from shaking is approximately $2.8 billion per year, with 32% of it occurring in Los Angeles County and 23% in the San Francisco-Oakland-Fremont metropolitan statistical area. This estimate reflects a 25% to 28% reduction because of changes in input ground motions. Scenario results indicate a 28% to 63% reduction in estimated building economic losses because of changes in input ground motions. Changes in input ground motions are mainly attributed to the use of next generation attenuation relations and, to a lesser extent, to updated earthquake source models and differing approaches for incorporating near-surface site effects.
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