9 First American Way - Soils Report

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Lutzky Associates Development, LP - Geotechnical Investigation MACTEC Projecl 4953-03-2631 September 18.2003 Tsunamis, Inundation, Seiches, and Flooding The site is located about 7 miles from the Pacific Ocean at an elevation of approximately 42 feet above mean sea level (U. S. Geological Survey datum). Therefore, tsunamis (seismic sea waves) are not considered a significant hazard at the site. According to the County of Orange Safety Element (1995), the site is not located downslope of any large bodies of water that could adversely affect the site in the event of earthquake-induced dam failures or seiches (wave oscillations in an enclosed or semi-enclosed body of water). The site is not within the limits of a 100-year fiood zone or a 500-year flood zone, based on flood maps published by FEMA (ESRUFEMA, 2003) Subsidence The site is not within an area of known subsidence associated with fiuid withdrawal (ground water or petroleum), peat oxidation, or hydrocompaction (City of Santa Ana General Plan, 1982). 5.6 ESTIMATED PEAK GROUND ACCELERATION Ground motions were postulated corresponding to the Design Basis EaMhquake (DBE), having a 10% probability of exceedence during a 50-year time period and the Upper Bound Earthquake (UBE), having a 10% probability of exceedence during a 100-year time period. The site-specific peak ground acceleration for the UBE was estimated by a Probabilistic Seismic Hazard Analysis (PSHA) using the computer program EZFRISK, Version 5.71. 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. The peak ground acceleration was estimated as the average of the ground motion attenuation relations for a "soil" site classification discussed in Abrahamson and Silva (1997), Boore et al. (1997), and Sadigh, et al. (1997). 14