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C:\TRICH\Jobs\4515582 Leprino Tracy\Report\Leprino Tracy CalARP 040221.docx 2-1 2. Seismic Hazard 2.1 Site Conditions In the absence of a detailed soils report, the previous CalARP evaluation used the 2013 California Building Code (CBC) (Reference 3) default presumptive load bearing values (Section 1806) and default soil profile (Section 1613.3.2). The allowable soil bearing pressure used in the previous seismic calculations was 1,500 psf. The soil profile used in the previous seismic design calculations was judged to be SD for stiff soils. The same soil profile and allowable soil bearing pressure are used for this revalidation. The site is along the western edge of a deep sedimentary trough stretching 400 miles though the center of the state. A previous report dated March 1999 references a March 1970 soils report by Dames & Moore stating that the upper two or three feet of soil are very stiff dark brown clay over eight to 12 feet of firm sandy and silty clay. Layers below are reported to be interbedded layers of silty sand, sandy silty clay, poorly graded sand and gravely sand with ground water encountered at seven to eight feet below the surface. Although a shallow groundwater table required for liquefaction exists at this site, the clays and sands with high silt and clay content greatly reduce this risk. 2.2 Site Seismic Hazard The City of Tracy, like much of the neighboring San Francisco Bay Area, is vulnerable to seismic activity due to the presence of several active earthquake faults in the region. The closest, and most prominent active faults near the City that have historically been the source of earthquakes felt in the vicinity include the Great Valley, San Andreas, Greenville, Calaveras, Hayward, and Mount Diablo Faults. Of these, the Great Valley Fault is closest. Its mapped trace is as close as 5 miles west of the site. The details of the controlling faults are shown in Figure 2-1 and summarized in Table 2-1 using data generated by CoreLogic, Inc.’s proprietary software, RQE® (Reference 10). In addition to prominent earthquake faults in the region, several faults with evidence of Quaternary activity (i.e., within the past 1.6 million years) have been identified in the vicinity. Figure 2-1 shows the location of these faults as mapped by the California