When the Big One Strikes Again—Estimated Losses due to a Repeat of the 1906 San Francisco Earthquake

Abstract

This paper presents interim results of an ongoing study of building damage and losses likely to occur due to a repeat of the 1906 San Francisco earthquake, using the HAZUS technology. Recent work by Boatwright et. al. (2006) provides MMI-based ShakeMap estimates of spectral response accelerations derived from observations of intensities in the 1906 San Francisco earthquake. This paper calculates damage and loss estimates using those estimated ground motions, then compares the resulting estimates with those calculated using a method parallel with that of current seismic provisions of building codes for a magnitude M7.9 event on the San Andreas Fault, and contrasts differences in damage and loss patterns for these two scenarios. The study region of interest comprises 19 counties of the greater San Francisco Bay Area and adjacent areas of Northern California, covering 24,000 square miles, with a population of more than ten million people and about $1.5 trillion of building and contents exposure. The majority of this property and population is within 40 km (25 miles) of the San Andreas Fault. The current population of this Northern California region is about ten times what it was in 1906, and the replacement value of buildings is about 500 times greater. Despite improvements in building codes and construction practices, the growth of the region over the past 100 years causes the range of estimated fatalities, approximately 800–3,400 depending on time of day and other variables, to be comparable to what it was in 1906. The forecast property loss to buildings for a repeat of the 1906 earthquake is in the range of approximately $90–120 billion; 7,000–10,000 commercial buildings in the region are estimated to be closed due to serious damage; and about 160,000–250,000 households calculated to be displaced from damaged residences. Losses due to fire following earthquake, as well as losses to utility and transportation systems, would be in addition to these estimates.