Landslide risk in the San Francisco Bay region

Abstract

We have used historical records of damaging landslides triggered by rainstorms, and a newly developed Probabilistic Landslide Assessment Cost Estimation System (PLACES), to estimate the numbers and direct costs of future landslides in the San Francisco Bay region. The estimated annual cost of future landslides in the entire region is about US $15 million (year 2000 $). The estimated annual cost is highest for San Mateo County ($3.32 million) and lowest for Solano County ($0.18 million). Normalizing costs by dividing by the percentage of land area with slopes equal or greater than about 10o indicates that San Francisco County will have the highest cost per square km ($7,400), whereas Santa Clara County will have the lowest cost per square km ($230). These results indicate that the San Francisco Bay region has one of the highest levels of landslide risk in the United States. Compared to landslide cost estimates from the rest of the world, the risk level in the Bay region seems high, but not exceptionally high.