Scenario and Annualized Earthquake Loss Estimation For the San Francisco Bay Area

The U.S. Geological Survey (USGS)-led Working Group on California Earthquake Probabilities (WG) has identified, and quantitatively assigned earthquake probabilities to, the major faults within the greater San Francisco Bay Area (SFBA). Using the Working Group fault characterization and HAZUS, the Federal Emergency Management Agency (FEMA)’s earthquake loss estimation model, we have made estimates of future losses within the SFBA due to ten potentially damaging scenario earthquakes in the region. In another study, the USGS, jointly with the California Geologic Survey (CGS), has recently completed and released the National Probabilistic Seismic Hazard Analysis (PSHA) maps. We have used the results of the PSHA maps for the State of California to make an estimate of the ground motion-induced annualized socio-economic losses in the SFBA. A summary of our loss estimates for the ten most likely damaging earthquakes forecast, as well as our annualized loss estimations are presented in this paper.In regard to the scenario loss estimation, we find that seven of the ten forecast earthquakes would cause social and economic disruptions in SFBA at least comparable to the 1989 Loma Prieta earthquake. The expected losses for the ten scenario events range from roughly $6 billion to $54 billion. Concerning the annualized losses, the estimate for the economic losses brought about by damage to buildings is about three quarter billion dollars annually. This is equivalent to a per-capita loss of $120 per year, or an annual reduction of the building value of 0.2%. HAZUS, due to its incomplete and inadequately detailed inventory and loss estimation methodology, does not reliably calculate damages to many major facilities and lifelines, such as water systems, light-rail systems, and ports.For this reason, we have focused our efforts on the analysis and evaluation of losses due to building damage. Scenario loss estimates pertain to relatively small regions neighboring hazardous faults. Hence, within the context of earthquake risk reduction, they should be used for mitigation and response planning for specific regions. Annualized loss estimates, on the other hand, reflect the long-term and regional impacts of earthquakes. Therefore, they can be best used for mitigation planning, prioritizing resources, code development and enforcement, and development of earthquake insurance policies for the long-term and on regional basis.