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Mr. Robert Evans Pr ;ct B02-02.03 January 30, 1991 Page 2 Identifying faults and seismic sources capable of generating earthquakes that may affect the site in a 100 -year period was the initial step in developing MCE estimates. To accomplish this, faults within 100 kilometers (km) of the site, which are considered to have been active in Late Quaternary time (i.e., the last 300,000 to 500,000 years), were evaluated based on a review of publications pertaining to the geology and tectonics of the region (Jennings, 1975; Real et al., 1987; and Wesnousky, 1986). The 100 -km radius was selected based on California Department of Mines and Geology (CDG) guidelines (1975). Numerous significant faults and fault zones are located within 100 km of the French Camp site (see Figure 1). Pertinent seismic sources include faults of both the Sierra Nevada and northern coast ranges geomorphic provinces. The Stockton and Midland fault zones within the Great Valley geomorphic province are the nearest faults to the site. However, neither fault exhibits evidence of late Quaternary displacement, so they were not subjected to analysis for the French Camp Landfill. The Quaternary Black Butte fault which is approximately 35 km west of the site is not considered as significant as the larger previously men- tioned faults. Significant Quaternary faults within a 50 -km radius of the site in- clude the Greenville, Midway, Tesla, and Antioch faults. Significant faults outside a 50 -km radius of the site include the Bear Mountain and Melones fault zones of the Sierra Foothill fault system to the east and the Hayward, Calaveras, and Livermore faults to the west. Slightly beyond the 100 - km radius is the San Andreas fault. Historical seismicity within 100 km of the site was compiled (see Figure 2) and indicates that the area surrounding the site is characterized by relatively low seismicity. Between 1900 and 1974, the epicenters for six significant historic earthquakes have been identified within 100 km of the site (Real et al., 1978). Maximum historic earthquakes for previously identified faults are summarized in Table 1. The maximum historic earthquake for the most significant seismic event is associated with the Greenville fault (magnitude 5.9), which occurred in 1980 approximately 39.5 km west of the site. The next significant seismic event oc- curred along the Antioch fault (magnitude 6.0) in 1889, approximately 47 km from the site (Real et al., 1978). To the east of the site the maximum historic earth- quake is associated with the Melones fault zone (magnitude 4.0), which occurred in 1937 approximately 136 km southeast of the site. Prior to 1975, the Sierra Foothills fault system (i.e., Bear Mountain and Melones fault zones) was consid- .0 ..� �11 I �