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2.7.3 Faulting <br />Based on our review of geologic and Earthquake Fault Zone maps, the subject site is not <br />located within a Special Studies Zone (Hart and Bryant, 1997) and no active faults are <br />mapped projecting through the subject site. The possibility of damage due to ground rupture <br />from earthquake fault rupture is considered low since active faults are not known to cross the <br />site. <br />Secondary effects of seismic shaking resulting from large earthquakes on the major faults in <br />the southern California region, which may affect the site, include soil liquefaction and <br />dynamic settlement. Other secondary seismic effects include shallow ground rupture, and <br />seiches and tsunamis. In general, these secondary effects of seismic shaking are a possibility <br />throughout the Southern California region and are dependant on the distance between the site <br />and causative fault and the onsite geology. The major active faults that could produce these <br />secondary effects is the Elsinore -Whittier, Newport -Inglewood, and San Andreas faults, <br />among others, surround the site. <br />A discussion of liquefaction and these secondary effects is provided in the following sections. <br />2.7.4 Shallow Ground Rupture <br />Shallow ground rupture due to active faulting is not likely to occur on site due to the distance <br />from likely seismic events. Therefore, this phenomenon is not considered a significant <br />hazard, although it is a possibility at any site. <br />2.7.5 Liquefaction and Dry Sand Settlement <br />Liquefaction is a seismic phenomenon in which loose, saturated, granular soils behave <br />similarly to a fluid when subject to high -intensity ground shaking. Liquefaction occurs when <br />three general conditions exist: 1) shallow groundwater; 2) low density non -cohesive <br />(granular) soils; and 3) high -intensity ground motion. Liquefaction is typified by a buildup <br />of pore -water pressure in the affected soil layer to a point where a total loss of shear strength <br />occurs, causing the soil to behave as a liquid. Studies indicate that saturated, loose to medium <br />dense, near surface cohesionless soils exhibit the highest liquefaction potential, while dry, <br />dense, cohesionless soils and cohesive soils exhibit low to negligible liquefaction potential. <br />Based on a review of seismic hazard zone map for the Tustin Quadrangle and Orange <br />Quadrangle prepared by the California Geological Survey (CGS, 2002), the site is not located <br />within a State of California Seismic Hazard Zone mapped liquefaction hazard area. Effects of <br />liquefaction on level ground include potential seismic settlement, sand boils, ground <br />oscillation, and bearing capacity failures below structures. <br />Historic high groundwater elevation is greater than 40 feet below the ground surface near the <br />location of the subject site (CGS, 2002). No groundwater was encountered in the borings to a <br />depth of 51.5 feet. A conservative groundwater depth of 40 feet was utilized in the <br />liquefaction analysis. <br />Project i y ouncil 18 — 822 1 3 , 2021 <br />