HR: 0800h
AN: T41C-1239    [Abstracts]
TI: Basement Control of Fault Orientation and Style of Deformation Along the Active Strike-Slip Boundary of the Inner Southern California Borderland, Gulf of Santa Catalina
AU: * Conrad, J E
EM: jconrad@usgs.gov
AF: U.S. Geological Survey, 345 Middlfield Rd., MS 999, Menlo Park, CA 94025 United States
AU: Ryan, H F
EM: hryan@usgs.gov
AF: U.S. Geological Survey, 345 Middlfield Rd., MS 999, Menlo Park, CA 94025 United States
AU: Sliter, R W
EM: rsliter@usgs.gov
AF: U.S. Geological Survey, 345 Middlfield Rd., MS 999, Menlo Park, CA 94025 United States
AB: Although the active faults of the inner southern California borderland south of Los Angeles appear to comprise a relatively simple system of northwest-trending strike-slip faults, closer inspection of these faults reveals a more complicated fault pattern than might be expected from models of simple shear. The major fault systems of the inner borderland include the Palos Verdes, Coronado Bank, Newport-Inglewood-Rose Canyon, and San Diego Trough fault zones. Seismic reflection profiles show that these fault zones extend over distances of 60-150 km and generally trend about N$30\deg$W, about $10\deg$ more northerly than predicted by relative Pacific-North America plate motions. The fault zones vary in structural style from the relatively simple, continuous San Diego Trough fault zone in the west, to more complicated fault zones to the east that are typically comprised of short, often multi-stranded, fault segments. These faults show significant variations in deformational style along strike, involving right and left stepovers, changes in fault orientation, and variations from transpressive to transtensive faulting. Structures adjacent to these faults also appear to show complicated histories. A comparison between the location of active fault traces with respect to prominent, partly subsurface, basement ridges and knolls composed of middle Miocene and older rocks show that the pre-existing basement ridges partly control the deformational style of modern fault-related structures. The ridges themselves are probably relict features of early to middle Miocene extension and related volcanism.
DE: 7223 Seismic hazard assessment and prediction
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8105 Continental margins and sedimentary basins
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting