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<br /> <br />Red Morton Community Park Sports Lighting Initial Study <br />City of Redwood City 38 June 2015 <br />4.6 GEOLOGY AND SOILS <br /> <br />4.6.1 Setting <br /> <br />4.6.1.1 Regional Geology <br /> <br />The City of Redwood City is located in the seismically active San Francisco Bay Area. Due to its <br />location near the boundary between the North American and Pacific tectonic plates, the Bay Area is <br />exposed to geologic and seismic hazards such as earthquake fault ruptures, strong seismic ground <br />shaking, and seismic‐related ground failure, including liquefaction and landslides. <br /> <br />Although mapping completed under the Alquist‐Priolo Earthquake Fault Zoning Act indicates that no <br />active earthquake fault zones are located in the City, several major region al active fault zones are of <br />concern. The San Andreas Fault zone–a significant tectonic feature–is located approximately 2,000 <br />feet southwest of Redwood City. The active San Gregorio‐Seal Cove Fault lies 9.5 miles to the west <br />of Redwood City, and the inactive Pilarcitos fault located roughly two miles to the west. Other major <br />regional active faults include the Hayward, Rodgers Creek, Calaveras, West Napa, Green Valley, <br />Concord, and Greenville faults. <br /> <br />4.6.1.2 Soils <br /> <br />Soils on the project site consist of Orthents, cut and fill and Urban-land Orthents, cut and fill <br />complex. Because these soils consist largely of cut and fill materials, the expansion potential is <br />unknown.12 <br /> <br />4.6.1.3 Liquefaction <br /> <br />Liquefaction is the result of seismic activity and is characterized as the transformation of loose, <br />water-saturated soils from a solid state to a liquid state after ground shaking. There are many <br />variables that contribute to liquefaction, including the age of the soil, soil type , soil cohesion, soil <br />density, and ground water level. Flow failure, lateral spreading, differential settlement, loss of <br />bearing strength, ground fissures, lurch cracking, and sand boils are caused by liquefaction. The <br />project site is located within a liquefaction hazard zone.13 <br /> <br /> <br /> <br />12 United States Department of Agriculture, Natural Resources Conservation Service. Web Soil Survey. <br />http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm. Accessed April 7, 2015. <br />13 Association of Bay Area Government. Interactive Seismic Hazards Zone Map. <br />http://resilience.abag.ca.gov/earthquakes/. Accessed April 7, 2015. <br />8.A. - Page 55