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File No. A7-1909-J1 ` November 3, 1987 I � discontinuous layers of silts, sands a d clays interbedded with gravel horizons. Literature and Map Review: The literature indicates that bedrock in this vicinity is located at a depth greater tt an 50 feet beneath the surface (California Department of Water Resources, 1967). Seismic History of the Area : No active faults are known to exist within the subject site. The nearest active fault is the Greenville, which is located approximately 9 miles southwest of the site. The buried trace of the Tracy Fault, shown by Jennings to be Quaternary in age is approximately 2 miles to . the north. Other active faults are the Calaveras, Hayward and San Andreas, �;4 which are approximately 25, 30 and 48 miles, respectively, of the site. ,� The last major earthquake on the San Andreas fault occurred on April 18, 1906. Its epicenter was located in Marin County, approximately 60 miles northwest of �.� the site, with a magnitude of 8.3 on the Richter scale. Extensive damage was reported throughout the San Francisco Bay area (Lawson, 1908) . There have been at least two major earthquakes on the Hayward fault in historic times, 1836 and 1868. The most recent earthquake attributed to the Calaveras fault 'E occurred in 1984 with a magnitude of 6.2, centered approximately ten miles northeast of the Morgan Hill . That earthquake caused considerable damage to structures in the Morgan Hill area. The Calaveras is considered capable of ' producing earthquakes of the same magnitude as the Hayward fault, up to 7.5 on ` the Richter scale. The Greenville has a reported maximum estimated magnitude of 6.6. In 1980 a 5.8 magnitude earthquake on the Greenville fault caused considerable damage in the Livermore area. The effects of major concern at this site are damage relating to ground shaking and ground failure resulting fro a moderate to major ' earthquake centered on one of the Bay Area's active aults. The term ground failure' encompasses several different effects. Various organizations indicate that the potential hazards from liquefaction, including lateral spreading, differential subsidence and lurch crackinc could affect this site. 1.7 p , a Conclusions t 1. Based on the results of this preliminary investigation, we conclude { that it is feasible, from a geotechnical viewpoint, to construct the proposed one- and/or two-stor r din s at the subject M site, assuming a final soil investigation is performed and the recommendations of that soil investigation are followed. 2. The undisturbed native soils appear to have adequate strength to support any shallow structural fil s and proposed structures without detrimental settlements. It is anticipated that the one- and two-story structures can be supported by sha low conventional spread and strip foundations, or a drilled, poured-'n-place, concrete, friction pier and tY grade beam foundation system. 3. The near-surface soil exhibits a moderate to high shrink-swell (expansive) potentials. Mitigating measures, such a increased t- foundation trenching depths, the utilization of pier and grade beam ,4 4 Applied soil Mechanics