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ENGEO <br /> INCORPORATED <br /> <br /> <br />5150.100.101 <br />May 2, 2008 Page 10 <br />An existing driveway and 25-foot-wide setback zone are located between the potential landslide <br />area and the proposed building location. This intervening area will serve as a debris catchment <br />area in the event of seismically induced landsliding. <br /> <br />5.4.5 Liquefaction <br /> <br />Liquefaction is a phenomenon in which saturated cohesionless soils are subject to a temporary, <br />but essentially total, loss of shear strength because of pore pressure build-up under the reversing <br />cyclic shear stresses associated with earthquakes. As noted above, the site is located within a <br />preliminary State of California Seismic Hazard Zone for areas that may be susceptible to <br />liquefaction. Relatively shallow bedrock was encountered on the eastern portion of the site and <br />the thicker colluvial soils that were encountered on the western portion of the side consist of <br />clayey soils. Based on the subsurface conditions encountered in our exploration, it is our opinion <br />that liquefaction at the site during strong earthquake shaking is unlikely. <br /> <br />5.4.6 Lurching <br /> <br />Ground lurching is a result of the rolling motion imparted to the ground surface during energy <br />released by an earthquake. Such rolling motion can cause ground cracks to form in weaker soils. <br />The potential for the formation of these cracks is considered greater at contacts between deep <br />alluvium and bedrock. Recommendations for foundation and pavement design provided in this <br />report are intended to reduce the potential for adverse impacts from lurch cracking <br /> <br />5.4.7 Densification Due to Earthquake Shaking <br /> <br />Densification of sandy soils above and below the groundwater level can cause settlement during <br />an earthquake. Based on the soil and geologic data analyzed for this site, densification due to <br />ground shaking is unlikely.