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Table 4.7-2 <br /> 1998 California Building Code -Seismic Source Type <br /> Seismic Seismic Source Description Seismic Source Definition <br /> Source Type Maximum Moment Magnitude, M Slip Rate,SR(mm/year) <br /> A Faults that are capable of producing M * 7.0 SR * 5 <br /> large-magnitude events that have a <br /> high rate of seismic activity <br /> B All faults other than Types A and C M*7.0 SR<5 <br /> M<7.0 SR>2 <br /> M*6.5 SR<2 <br /> C Faults that are not capable of M<6.5 SR*2 <br /> producing large-magnitude <br /> earthquakes and that have a relatively <br /> low rate of seismic activity <br /> Source: 1998 California Building Code <br /> GROUND FAILURE/LIQUEFACTION <br /> Liquefaction is a process by which water-saturated materials(including soil, sediment, and certain types of <br /> volcanic deposits) lose strength and may fail during strong ground shaking. Liquefaction is defined as "the <br /> transformation of a granular material from a solid state into a liquefied state as a consequence of increased pore- <br /> water pressure"(Youd 1992). This behavior is most commonly induced by strong ground shaking associated with <br /> earthquakes. In some cases, a complete loss of strength occurs and catastrophic ground failure may result. <br /> Soil liquefaction occurs when ground shaking from an earthquake causes a sediment layer saturated with <br /> groundwater to lose strength and take on the characteristics of a fluid,thus becoming similar to quicksand. There <br /> are four types of ground failure or collapse of soil structures that commonly result from liquefaction: lateral <br /> spread, flow failure,ground oscillation, and loss of bearing strength. <br /> One consequence that may result from the occurrence of liquefaction is an associated surface expression. If the <br /> seismic event occurs over an extended duration,the liquefied soils may migrate toward the surface,resulting in <br /> ejection and subsequent sand boiling at the surface. <br /> Liquefaction poses a hazard to engineered structures. The loss of soil strength can result in bearing capacity <br /> insufficient to support foundation loads,increased lateral pressure on retaining or basement walls, and slope <br /> instability. Factors determining the liquefaction potential of a given site are soil type,the level and duration of <br /> possible seismic ground motions,the type and consistency of soils, and the depth to groundwater. Loose sands <br /> and peat deposits are susceptible to liquefaction,whereas clayey silts, silty clays, and clays deposited in fresh <br /> water environments are generally stable under the influence of seismic ground shaking.Age also is a factor in the <br /> potential of soils to liquefy,with Holocene deposits (from approximately the last 10,000 years)being the most <br /> sensitive to liquefaction. <br /> According to the geotechnical engineering report for the Wastewater Quality Control Facility(WQCF) site <br /> prepared by Kleinfelder(1997),groundwater was encountered in borings at depths of 8 to 12 feet below the <br /> existing site grade. In previous investigations, groundwater was encountered as high as three feet below grade. <br /> Based on field explorations, laboratory tests, and engineering analysis,the report found that the potential for <br /> liquefaction at the site exists. In addition,the report also states that the potential for differential settlement of <br /> surface structures due to liquefaction beneath the site is high due to the presence of loose clean sands and high <br /> groundwater. In a 2004 addendum to the 1997 report, it is reported that the potential for liquefaction generated by <br /> more distant faults to the east,west, and southwest is considered remote. However,test results show that <br /> EDAW Manteca WQCF and Collection System Master Plans EIR <br /> Geology, Soils,and Seismicity 4.74 City of Manteca <br />