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GEOSYNTEC CONSULTANTS Dr. Hari Sharma, P.E., G.E. 22 January 2001 Page 4 landfill site. The PHGA estimates were obtained using the Abrahamson and Silva [ 1997) attenuation model. The D, estimates were obtained using the Abrahamson and Silva (1996) duration model. Table l indicates that the MW 6.4 MPE event on the Great Valley blind thrust system at a distance of 21mi (34 km) induces the highest bedrock MPE PHGA at the site. Table 1 further indicates that the Mw 6.7 MCE event on the Great Valley blind thrust system at a distance of 21mi (34 km) induces the. highest bedrock MCE PHGA at the site. Table I also indicates that the MPE and MCE on the San Andreas fault system are characterized by the same Mme, 7.9 event at a distance of 70 mi (112 km). This large - magnitude distant event induces the longest duration of strong ground shaking at the site. Given a relatively small difference in the estimated bedrock PHGA and the relatively large difference in estimated D.,, the MW 7.9 event on the San Andreas fault system may be the most damaging earthquake for the Forward Site. Therefore, the K, 7.9 event on the San Andreas fault system should be considered for evaluation of both. ME and MCE design ground motions at the Forward Landfill site along with the appropriate Mu, event on the Great Valley blind thrust system. Evaluation of Design Ground Motions Acceleration time histories (accelerograms) representative of both candidate MPE and MCE events (M,v 6.4 MPE or MW 6.7 MCE event at the Great Valley fault system and MPE/MCE MW 7.9 at the San Andreas fault system) are required for use in seismic response and deformation analyses at the Forward Landfill site. GeoSyntec selected a suite of four design time histories on the basis of the following methodology: (i) screen the database of acceleration time histories on the basis of earthquake magnitude and predominant style of faulting and develop a reduced database of time histories that were recorded in events similar to these of the WE; (ii) screen the reduced set of acceleration time histories based on the target duration of strong ground shaking; and (iii) plot the acceleration response spectra of selected accelerograms against target acceleration response spectra and select a suite of time P: IPRJ21 CAWPWOC.!L!F-WC1FORWARDIFOR-HAZ. DOC C •