9 First American Way - Soils Report

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Lutzky Associates Development, LP - Geolechnical Investigation MACTEC Project 4953-03-2631 September 18. 2003 6.6 TIME HISTORIES Spectral Matching Procedure The computer program RSPMATCH (Abrahamson, 1998) was used to perform time-domain spectral matching ofÂ¥ seven orthogonal sets of horizontal time hi@ories. The spectral matching procedure modifies the empirically recorded (initial) time histories usually by adding a tapered cosine wave so that the response spectrum of the modified time history and the target spectrum match. For each period, the time of the maximum response is computed for the initial (unmodified) time history. A tapered cosine wave is then added at that computed time to either increase or decrease the spectral response and match the target spectrum for the specific period. The initial phasing of the time history can be maintained because the modification for each period is applied at the time of maximum spectral response rather than throughout the entire time history, as is done in frequency-domain spectral matching. The spectral matching was performed for the DBE and the UBE design response spectra with 5% damping. Spectral Matching Procedure We performed spectral matching for the DBE and UBE level earthquake in accordance with the Appendix 16A of the California Building Code, 2001 edition. De-aggregation results for the PGA (zero spectral period) indicate that seismic events from strike-slip and reverse-oblique faults with magnitudes ranging from 5 to 7 at distances of about six kilometers or nearer are the predominant contributors to the seismic shaking hazard of the project site. The seven time histories selected for matching are presented in Table 6, Empirical Time Histories Selected for Spectral Matching. These records were selected based on the following factors: robust long-period content, inclusion of strong directivity or near-source ground motions, and the results of de-aggregation of probabilistic seismic hazard. 23