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GEOSmrsC CoNSULTA n <br /> Dr. Hari Sharma, P.E., G.E. <br /> 22 January 2001 <br /> Page 4 <br /> landfill site. The PHGA estimates were obtained using the Abrahamson and Silva <br /> [1997) attenuation model. The DS estimates were obtained using the Abrahamson and <br /> Silva (1996) duration model. Table l indicates that the MW 6.4 MPE event on the Great <br /> Valley blind thrust system at a distance of 21mi (34 km) induces the highest bedrock <br /> WE PHGA at the site. Table I further indicates that the MW 6.7 MCE event on the <br /> Great Valley blind thrust system at a distance of 21mi (34 km) induces the.highest <br /> bedrock MCE PHGA at the site." <br /> Table 1 also indicates that the WE and MCE on the San Andreas fault system <br /> are characterized by the same MW 7.9 event at a distance of 70 mi (112 km). This large- <br /> magnitude distant event induces the longest duration of strong ground shaking at the <br /> site. Given a relatively small difference in the estimated bedrock PHGA and the <br /> relatively large difference in estimated DS, the MW 7.9 event on the San Andreas fault <br /> system may be the most damaging earthquake for the Forward Site. Therefore, the M„, <br /> 7.9 event on the San Andreas fault system should be considered for evaluation of both. <br /> OE and MCE design ground motions at the Forward Landfill site along with the <br /> appropriate M,�event on the Great Valley blind thrust system. <br /> Evaluation of Design Ground Motions <br /> Acceleration time histories (accelerograms) representative of both candidate <br /> WE and MCE events (M,,, 6.4 WE or M,r 6.7 MCE event at the Great Valley fault <br /> system and MPE/MCE M,,.7.9 at the San Andreas fault system) are required for use in <br /> seismic response and deformation analyses at the Forward Landfill site. GeoSyntec <br /> selected a suite of four design time histories on the basis of the following <br /> methodology: (i) screen the database of acceleration time histories on the basis of <br /> earthquake magnitude and predominant style of faulting and develop a reduced database <br /> of time histories that were recorded in events similar to these of the WE; (ii) screen <br /> the reduced set of acceleration time histories based on the target duration of strong <br /> ground shaking; and (iii) plot the acceleration response spectra of selected <br /> accelerograms against target acceleration response spectra and select a suite of time <br /> P:lPRJ71CAWPWX iC,4L/F-WCIFORWARDIFOR-H,4ZDOC <br /> ti <br />