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File No. 20-1008-48 kn KLEINFELDER January 3 , 1992 fault and the Tracy-Stockton fault. Neither of these faults is located near the site, and there is no evidence to suggest that either fault is likely to cause surface displacement in the site area. The major faults which have historically produced earthquakes of greatest magnitude in central California are the Calaveras, Hayward, and San Andreas faults in the Coast Ranges; the Greenville and Midland (suspected) faults on the west side of the Great Valley; and the Sierra Nevada and Owens Valley faults east of the Sierra Nevada mountains. Local faults include numerous small shear zones and two major fault zones, the Bear Mountains and Melones, which make up the Foothills fault system. A map showing the locations of the major faults of central California, in relation to the site, is presented on Plate A-11 of this report. A map showing the locations of historical earthquakes with Richter magnitudes greater than 5. 0 that occurred between 1800 and 1990 within approximately 100 miles of the site is presented on Plate A-12 of this report. In the past, the Foothills fault system has been considered inactive, with no known creep or displacement of geologic features ' since late Tertiary time. On August 1, 1975, a earthquake of magnitude 5.7 occurred approximately 6 miles southeast of Oroville. As a result of this event and subsequent aftershocks, a reevaluation of the potential activity of the Foothills fault system took place. It has been proposed that a 6. 5 magnitude earthquake may occur almost anywhere in the Foothills fault system. The Maximum Credible Earthquake (MCE) is defined as "the maximum earthquake that appears to be reasonably capable of occurring under the conditions of the presently known `geologic framework. "' The Maximum Probable Earthquake (MPE) is defined as "the maximum earthquake that appears to be reasonably expectable within a 100-year period. " Ground accelerations anticipated to be associated with the MCE's and MPE's, presented on Table I at 'the end of this report, are derived from attenuation relationships developed by Donovan and Bornstein (1978) . LIQIIEFACTION POTENTIAL The analysis of the liquefaction potential for sediments beneath the site follows procedures outlined by Seed and Idriss. Soils most susceptible to liquefaction are uniformly graded soils and of these soils, fine sands tend to liquefy more easily than do coarse sands, gravelly soils, silts or clays. Other factors involved with liquefaction potential are the relative density of the soils, the amount and type of overburden, the shape and arrangement of soil particles, groundwater elevation, and seismic Copyright 1992 Kleinfelder, Inc. Page 5 of 9