Probabilistic Warning Times for Earthquake Ground Shaking in the San Francisco Bay Area

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Current earthquake mitigation in the United States focuses on long-term characterization of the likely levels of ground shaking and the frequency of occurrence (Frankel et al. , 1996). These estimates are the basis for building codes, which aim to prevent collapse during earthquakes. In other countries, including Mexico, Japan, Taiwan, and Turkey, earthquake warning systems (EWS) are used in addition to building codes to further reduce the impact of earthquakes (Espinosa Aranda et al. , 1995; Wu et al. , 1998; Wu and Teng, 2002; Erdik et al. , 2003; Odaka et al. , 2003; Boese et al. , 2004; Kamigaichi, 2004; Nakamura, 2004; Horiuchi et al. , 2005; Wu and Kanamori, 2005). Short-term mitigation actions are taken to reduce both financial losses and casualties. Earthquake warning systems rapidly detect the initiation of earthquakes and warn of the forthcoming ground shaking. For a specific city, such as San Francisco, the warning time could be tens of seconds for some earthquakes but essentially zero seconds for others. Even in situations when San Francisco has zero seconds warning, however, neighboring cities such as Oakland would likely have a few seconds and San Jose would have ∼15 seconds warning. Thus, for any earthquake scenario in a densely populated region, such as the San Francisco Bay area (SFBA), an EWS could provide warning to at least some of the affected population in a damaging earthquake. Here I present estimates of the warning times that would be available for locations across the SFBA if an EWS were implemented in northern California. These warning times are calculated for identified likely earthquake scenarios in northern California. For each scenario an estimate of the probability of occurrence has been made (WGCEP, 2003), allowing calculation of probabilistic warning times. The …