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III. Environmental Setting, Impacts,and Mitigations <br /> J. Geology, Soils and Seismicity <br /> Seismic Hazard <br /> None of the known fault lines in San Joaquin County are classed as active faults,although <br /> historical epicenters have been located in the vicinity. Therefore,ground rupture is not <br /> considered a likely hazard on the project site,but ground shaking and any secondary effects of <br /> groundshaking would be probable seismic hazards. While surface rupture is normally restricted <br /> to areas along the fault(for earthquakes larger than M 5.5),ground shaking may affect areas for <br /> hundreds of miles around the fault. The intensity of ground shaking at a particular site is <br /> dependent on several factors including:earthquake magnitude,distance from the epicenter,and <br /> site conditions such as soil and rock types,geologic structure,and soil moisture conditions. <br /> Secondary hazards related to seismic events are indirectly associated with ground movement and <br /> include lurch cracking,liquefaction,differential settlement and slope failures. Indirect seismic <br /> hazards often occur when constructed structures or facilities fail due to seismic motion. <br /> The factors affecting the severity of ground shaking are those controlling earthquake intensity <br /> experienced at a particular location,although larger magnitude earthquakes generally cause the <br /> ground to shake harder and longer, and affect larger areas. Ground surface acceleration is the <br /> horizontal and vertical acceleration of the earth surface during an earthquake that results in <br /> ground motions.The duration of strong motion also varies,but averages approximately 18 <br /> seconds for a M 6.5 earthquake and 24 seconds for M 7.0 event(Greensfelder, 1974). <br /> Ground and Slope Stability <br /> Although the natural topography is nearly level,existing and proposed cut and fill slopes could <br /> be subject to static or seismic instability. Herzog, a geotechnical firm,observed that creep or <br /> shallow slumping has occurred on the open area by the west edge of the existing landfill,which <br /> has exposed refuse at two locations(R.W. Beck and Associates, 1992). In addition,the bearing <br /> strength of the soils may be of importance to ground stability and static or seismic settlement, yet <br /> the bearing capacity of the existing foundation soils has not been quantified. <br /> III.J.9 <br />