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Mr. Jonathan Scharfinan Silver Stone Communities 10 June 2005 Page 2 TreadwelI&RoIIo deposits at the ground surface that extended from 3 to II feet deep. The soft silt was then underlain by stiffto hard silt and clay. The soft silt appears to' underlie the northern portion of both adjacent sites. Groundwater was encountered in two borings at 8 and 19 feet deep. The remainder of the borings did not encounter groundwater. The water in the two borings may represent a perched water table, and the groundwater level at the site will likely fluctuate seasonally several feet. REGIONAL SEISMICITY AND FAULTING The major active faults in the area are the San Andreas, San Gregorio, Hayward, and Calaveras Faults. These and other faults of the region are shown on Figure 2. For each of the active faults within 50 kilometers, the distance from the site and estimated maximum Moment magnitude! [Working Group on California Earthquake Probabilities (WGCEP) (2003) and Cao et al. (2003)] are summarized in Table 1. TABLE 1 Regional Faults and Seismicity ~1~~f;,Ii;f~t~i~~~li~~!~1~~);:;;f/'j\"~i'm~i!!~~mi~:.1i Total Calaveras 4.1 Mt. Diablo - MID 8.3 South Hayward 14 Total Hayward 13.8 Total Hayward-Rodgers Creek 14 Greenville 15.7 Hayward - South East Extension 22 Concord/Green Valley 28.6 Great Valley 6 29 Great Valley 7 31 North Hayward 35.7 Monte Vista-Shannon 41 San Andreas - 1906 Rupture 44 San Andreas - Peninsula 44 .",,'~'~:~~i~x::,/'.~t:~~IIA11t.~t~ West 6.93 Northeast 6.65 Southwest 6.67 Southwest 6.91 Southwest 7 .26 Northeast 6.94 South 6.40 Northwest 6.71 East 6.70 East 6.70 West 6.49 Southwest 6.80 Southwest 7.90 Southwest 7.15 Moment magnitude is an energy-based scale and provides a physically meaningful measure of the size of a faulting event. Moment magnitude is directly related to average slip and fault rupture area.