9 First American Way - Soils Report

Home Browse Search

Lutzky Associates Development, LP - Geolechnical Investigation MACTEC Project 4953-03-2631 September 18.2003 5.4 FAULTS The numerous faults in Southern California include active, potentially active, and inactive faults. The criteria for these major groups are based on criteria developed by the Califbrnia -Geological Supve*-*reviously-the- Cali fornia DivisGn 'o9s.*andiGESIBBP)-for the Alquist-Priolo Earthquake Fault Zoning Program (Hart, 1999). By definition, an active fault is one that has had surface displacement within Holocene time (about the last 11,000 years). A potentially active fault is a fault that has demonstrated surface displacement of Quaternary age deposits (last 1.6 million years). Inactive faults have not moved in the last 1.6 million years. A list of nearby active faults and the distance in kilometers between the site and the nearest point on the fault, the maximum magnitude, and the slip rate for the fault is given in Table 1. A similar list for potentially active faults is presented in Table 2. The faults in the vicinity of the site are shown in Figure 4. Active Faults Newport-Inglewood Fault Zone The closest active fault to the site is the North Branch segment of the Newport-Inglewood fault zone located approximately 7 miles to the southwest. This fault zone is composed of a series of discontinuous northwest-trending en echelon faults extending from Ballona Gap southeastward to the area offshore of Newport Beach. This zone is refiected at the surface by a line of geomorphically young anticlinal hills and mesas formed by the folding and faulting of a thick sequence of Pleistocene age sediments and Tertiary age sedimentary rocks (Barrows, 1974). Fault- plane solutions for 39 small earthquakes (between 1977 and 1985) show mostly strike-slip faulting with some reverse faulting along the north segment (north of Dominguez Hills) and some normal faulting along the south segment (south of Dominguez Hills to Newport Beach) (Hauksson, 1987). Investigations by Law/Crandall (1993) in the Huntington Beach area indicate that the North Branch segment of the Newport-Inglewood fault zone offsets Holocene age alluvial deposits in the vicinity of the Santa Ana River. Whittier Fault The active Whittier fault zone is located approximately 14 miles north-northeast of the site. The Whittier fault trends northwest along the south flank of the Puente Hills from the Santa Ana River 5