9 First American Way - Soils Report

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Lutzky Associates Development, LP - Geolechnical Investigation MACTEC Project 4953-03-2631 September 18.2003 the Transverse Ranges west of Tejon Pass on the north to the Mexican border and beyond on the south. Wallace (1968) estimated the recurrence interval for a magnitude 8.0 earthquake along the entire fault zone to be between 50 and 200 years. Sieh (1984) estimated a recurrence interval of 140 to 200 years. The 1857 Fort Tejon earthquake was the last major earthquake along the San Andreas fault zone in Southern California. Blind Thrust Fault Zones San Joaquin Hills Thrust Until recently, the southern Los Angeles Basin has been estimated to have a low seismic hazard relative to the greater Los Angeles region (Working Group on California Earthquake Probabilities, 1995; Dolan et al., 1995). This estimation is generally based on the fewer number of known active faults and the lower rates of historic seismicity for this area. However, several recent studies by Grant et al. (2000,2002) suggest that an active blind thrust fault system underlies the San Joaquin Hilli. This postulated blind thrust fault is believed to be a faulted anticlinal fold, parallel to the Newport-Inglewood fault zone (NIFZ) but considered a distinctly separate seismic source (Grant et al., 2002). The recency of movement and Holocene slip rate of this fault are not known. However, the fault, i f it exists, has been estimated to be capable of a Magnitude 6.8 to 7.3 earthquake (Grant et al., 2002). This estimation is based primarily on coastal geomorphology and age-dating of marsh deposits that are elevated above the current coastline. The vertical surface projection of the San Joaquin Hills Thrust is located approximately 0.8 mile south of the site at the closest point. This thrust fault is not exposed at the surface and does not present a potential surface fault rupture hazard. However, the San Joaquin Hills Thrust is an active feature that can generate future earthquakes. The California Geological Survey (2003) considers this fault to be active and estimate an average slip rate of 0.5 mrn/yr and a maximum magnitude of 6.6 for the San Joaquin Hills Thrust. Puente Hills Blind Thrust The Puente Hills Blind-Thrust fault system (PHBT) is defined based on seismic reflection profiles, petroleum well data, and precisely located seismicity (Shaw and others, 2002). This blind thrust fault system extends eastward from downtown Los Angeles to Brea (in northern Orange County) 7