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Earthquake seismic hazard for the county is potential ground shaking from these three large faults. Table 10-4 lists additional faults in the Bay Area. Figure 10-2 shows locations and event probabilities for Bay Area fault lines. Table 10-4. Additional Faults within a 50-Mile Radius Fault Approximate Distance (miles/direction) Calaveras 17 miles from East Palo Alto Greenville 23 miles from Menlo Park Mount Diablo Thrust 27 miles from South San Francisco Concord-Green Valley 30 miles from South San Francisco Rogers Creek (Part of Hayward Fault System) 35 miles from South San Francisco San Andreas Fault The San Andreas Fault is a transform boundary that spans 810 miles from the East Pacific rise in the Gulf of California through the Mendocino fracture zone off the shore of northern California. The fault is estimated to be 28 million years old. The San Andreas Fault is an example of a transform boundary exposed on a continent. The fault forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right- lateral strike-slip. The San Andreas Fault is typically referenced in three segments. The southern segment extends from its origin at the East Pacific Rise to Parkfield, California, in Monterey County. The central segment extends from Parkfield to Hollister, California. The northern segment extends northwest from Hollister, through San Mateo County, to its junction with the Mendocino fracture zone and the Cascadia subduction zone in the Pacific Ocean. The San Andreas Fault crosses the center of the county, passing through the population centers of Daly City and San Bruno and posing considerable risk for surface fault rupture within those cities. The San Andreas Fault has a 21 percent chance of generating a magnitude 6.7 or greater earthquake in the next 30 years. The last earthquake with a magnitude over 5.0 with an epicenter in San Mateo County was the 1957 Daly City earthquake, with a magnitude of 5.3. While the epicenter of the magnitude 7.8 earthquake in 1906 on the San Andreas Fault was not within the county, it still caused extreme ground shaking. A similar earthquake in the future would likely do the same, especially in the heavily populated Bayside, much of which is underlain by alluvial deposits, bay mud, and artificial fill. A rupture along the peninsula would cause extremely violent ground shaking throughout the county. The bay margins are likely to experience liquefaction in a major earthquake. Monte Vista-Shannon Fault The Monte Vista-Shannon fault zone is a predominantly a southwest-dipping oblique slip fault that extends about 28 miles along the northeastern margin of the Santa Cruz Mountains from the vicinity of Los Trancos Creek southeast to the Alamitos Creek area, near Calero Reservoir (USGS, 2020). Butano Fault The Butano Fault is a 23-mile-long fault that falls along Pescadero Creek in San Mateo County. It merges with the San Andreas fault from the northwest and the Sargent fault from the southeast. It appears t o have a symmetrical relation to the San Andreas fault and may have similar seismic potential (USGS, 1974). 10-7