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Earthquake Hayward Fault The Hayward Fault is a 45-mile-long fault that parallels the San Andreas Fault on the East Bay. The Hayward Fault extends through some of the Bay Area’s most populated areas, including San Jose, Oakland, and Berkeley. The Hayward Fault is a right lateral slip fault. The Hayward Fault has a 31-percent chance of producing a magnitude 6.7 or greater earthquake in the next 30 years. An earthquake of this magnitude has regional implications for the entire Bay Area, as the Hayward Fault crosses numerous transportation and resource facilities, such as highways and the Hetch Hetchy Aqueduct. Disruption of the Hetch Hetchy system has the potential to severely impair water service to San Mateo County. The Hayward Fault is increasingly becoming a hazard priority throughout the Bay region because of its increased chance for activity and its intersection with multiple highly populated areas and critical facilities. San Gregorio Fault The San Gregorio Fault is a northwest-trending right-lateral slip deformation near the western edge of San Mateo County, crossing briefly over uninhabited land in San Mateo County around Pillar Point at Half Moon Bay. The fault runs from southern Monterey Bay through Bolinas Bay, where its north section intersects with the San Andreas Fault offshore north of San Francisco. San Gregorio is the principal active fault west of the San Andreas for the Bay Area region. The San Gregorio Fault is one of the less studied fault lines, the result of its primary location offshore and its proximity to the better-known San Andreas Fault and Hayward Fault. Its probability of experiencing a magnitude 6.7 or greater earthquake within the next 30 years is 6 percent—significantly less than San Andreas Fault or Hayward Fault. However, the location of the fault poses a significant threat to San Mateo County. NEHRP Soil Type and Liquefaction Mapping Figure 10-3 shows NEHRP soil classifications in San Mateo County. Figure 10-4 shows areas that have moderate, high or very high susceptibility to liquefaction. Alquist-Priolo Zone Maps Alquist-Priolo zone maps provide regulatory zones for potential surface fault rupture where fault lines intersect with future development and populated areas. The purpose of these maps is to assist in the geologic investigation before construction begins to ensure that the resulting structure will not be located on an active fault. Daly City and San Bruno are located in designated Alquist-Priolo Zones for the San Andreas Fault. Alquist-Priolo maps were referenced, but not specifically used, in the assessment of risk for this plan as a result of the existence of current extensive studies and regulations and ongoing monitoring and update of Alquist-Priolo Zones by the State of California. This plan assumes that the studies conducted, and information provided by the State of California are the best available data for surface rupture risk and could not be improved through a separate assessment for this plan. Alquist-Priolo maps are available to the public at: http://maps.conservation.ca.gov/cgs/informationwarehouse/index.html?map=regulatorymaps. 10-9