9 First American Way - Soils Report

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Lutzky Associates Development. LP - Geotechnical Investigation MACTEC Project 4953-03-2631 September 18.2003 the near source factors, N. and â‚¬, are tb be ta-ken as 1.0 and 1.0 respectively, based bn Tables 16-S and 16-T of the CBC. 6.5 RESPONSE SPECTRA Ground motions were postulated corresponding to earthquake levels having a'-TO% probability of, *ded'*rite during a 30-year time period (dekignated the Design Basis Earthquake, DBE) and a 10% probability of exceedence during in a 100-year time period (designated the Upper Bound Earthquake, UBE). The probabilistic response spectra developed for this study are referred to as the site-specific response spectra. The site-specific response spectra for the DBE and UBE levels of shaking specified were determined by a Probabilistic Seismic Hazard Analysis (PSHA) using the computer program EZFRISK, Version 5.71. EZFRISK converts the slip rate of each fault into an activity rate using an algorithm consistent with the Anderson and Luco Occurrence Relation 2 (Anderson and Luco, 1983). The faults used in the study are shown in Tables 1 and 2, along with the maximum magnitude and the slip rate assigned to each fault. Please note that a recently released PSHA fault model (CGS, 2003) includes the San Joaquin Hills fault, a previously unknown blind thrust fault that underlies the San Joaquin Hills to the south of the site. We have included this fault in our PSHA model, resulting in higher estimated ground motion values in the region compared with previously released data. The response spectra were developed using the average of the attenuation relations discussed in Abrahamson and Silva (1997), Boore et al. (1997), and Sadigh, et al. (1997), for a "soil" site type with a shear wave velocity in the upper 30 meters equal to 234 meters per second. Dispersion in the ground motion attenuation relationships was considered by inclusion of the standard deviation of the ground motion data in the attenuation relationships used in the PSHA. We have used the relationships for rupture area versus magnitude of Wells and Coppersmith (1994) for selected faults in our model. The response spectra for the horizontal component of shaking for the DBE and UBE ground motions are shown on Figures 7 and 8 for structural damping values of 2%, 5% and 10%. The response spectra in digitized form are presented in Tables 4 and 5. 22