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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Geology,Soils,and Seismicity The project area is classified as Prime Farmland(see section 3.B,"Agricultural Resources, Land Use,and Planning,"for more information on the classes of agricultural soils and the definition of Prime Farmland). As stated in Chapter 2, "Project Description,"the project area is located on five parcels zoned AG40 (General Agriculture)and designated A/G(General Agriculture)in the San Joaquin County General Plan(Figure 2-3). The project area has been graded for agricultural use, and the majority of the site is currently in agricultural use as an almond orchard. Seismicity Seismic hazards refer to earthquake fault ground rupture and ground shaking — (primary hazards)and liquefaction and earthquake-induced slope failure (secondary hazards). Localized ground shaking and liquefaction are the most significant seismic hazards in San Joaquin County (San Joaquin County 1992). Surface Rupture and Faulting The project area is subject to seismic hazards because of its proximity to the San _ Andreas Fault Zone. Faults within the San Andreas Fault Zone are known to be historically active and are capable of generating earthquakes with sufficient magnitude to cause strong ground motion in the project area. However,the Uniform Building Code(UBC)recognizes no active seismic sources within the project vicinity(International Conference of Building Officials 1997),and no active faults are known to cross the project area. Several Holocene faults are located in an approximate 20-mile radius of the proposed project area. Because of documented recency of surface movement and the distribution of ongoing earthquakes along them, the Greenville and Ortigalita faults are considered active(Jennings 1994). Both of these faults are within Alquist-Priolo Earthquake Fault Zones (Hart and Bryant 1997). Of these, the Greenville Fault Zone is closest to the project area,located about 14-20 miles to the west. Several early Quaternary faults are present in an approximate 20-mile radius. These potentially active faults include the San Joaquin(a.k.a. Great Valley),Black Butte,Vemalis,Midway,and Stockton faults (Jennings 1994). — The Greenville Fault Zone includes several active segments. According to the Working Group on California Earthquake Probabilities(2003),the probability of — a Richter magnitude 6.7 or greater earthquake on the Greenville Fault Zone in the next 30 years is 3%. Specifically,the northern segment has a probability of 2.3%, and the southern segment has a probability of 2.1%. According to Peterson et al. (1996),the estimated probability for an earthquake of moment magnitudes of 6.9 on the Greenville Fault Zone in the next 30 years is 5.8%. Ground Shaking Hazard — The risk of surface rupture in the project area is generally low because of the relatively far distance to faults;however,earthquake-induced ground shaking poses a more serious threat. Most of the seismic activity in the vicinity of the — project area(and therefore most of the seismic ground shaking hazard) is DeSilva Gates Quarry Project — Draft Environmental Impact Report 3.F4 J8a 05105.05