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San Joaquin County Community Environmental Setting, Impacts,and Mitigation Measures Development Department Geology,Soils,and Seismicity associated with the historically active San Andreas Fault Zone,which includes several major active fault zones, including the Greenville, Calaveras,and Hayward Fault Zones. The greater the energy released from the fault rupture,the higher the magnitude of the earthquake. Earthquake energy is most intense at the fault epicenter;the farther an area is from an earthquake epicenter, the less the intensity of the ground shaking that occurs there. Geologic and soil units comprising unconsolidated,clay-free sands can reach unstable conditions during ground shaking, which can result in extensive damage to structures built on them(see Liquefaction and Related Hazards below). ►� Ground shaking is described by three methods: ground acceleration as a fraction of the acceleration of gravity(g); the Modified Mercalli scale, is a more descriptive method with intensities that range from I(shaking that is not felt)to XII(total damage); and the UBC Seismic Hazard Zone. The project area is located in a region of California characterized by high ground-shaking hazard. Based on a probabilistic seismic hazard map that depicts the peak horizontal ground acceleration values exceeded at a 10%probability in 50 years(California Geological Survey 2003; Cao et al. 2003), the probabilistic peak horizontal ground acceleration values for the project area range from 0.3- 0.48(where 1.0 g is the force of gravity). This indicates that the ground-shaking hazard in the project area is moderate, corresponding to a Modified Mercalli intensity of VIII—IX,for which damage to structures built to withstand ` earthquakes would be moderate. Further to the west,the ground-shaking hazard increases,coinciding with the increase in abundance of associated faults and fault complexes(California Geological Survey 2003; Cao et al.2003). The project area is located within UBC Seismic Hazard Zone 3. The Zone 3 designation indicates earthquakes in the region have the potential to make .. standing difficult and cause stucco and some masonry walls to fall. Structures must be designed to meet the regulations and standards associated with Zone 3 hazards. Liquefaction and Related Hazards Poorly consolidated,water-saturated fine sands located within 30-50 feet of the ` surface typically are considered to be the most susceptible to liquefaction. Soils and sediments that are not water saturated or that consist of coarser or finer materials are generally not susceptible to liquefaction(California Division of Mines and Geology 1997). Based on the appreciable clay content and absence of sands in project area substrates, as described above,and water table depths no shallower than 70 feet,liquefaction susceptibility is expected to be relatively low in the project area. DeSilva Gates Quarry Project Draft Environmental Impact Report 3.F-5 As 05105.05