HR: 0800h
AN: T51D-1362    [Abstracts]
TI: Active Fault Deformation Along the South Boundary of the Western Transverse Ranges Province, Point Dume to the Northern Channel Islands, Southern California
AU: * Fisher, M A
EM: mfisher@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025
AU: Langenheim, V E
EM: zulanger@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025
AU: Sorlien, C C
EM: chris@crustal.ucsb.edu
AF: Institute for Crustal Studies, UC Santa Barbara, Santa Barbara, CA 93106
AU: Nicholson, C
EM: nicholson@msi.ucsb.edu
AF: Marine Science Institute, UC Santa Barbara, Santa Barbara, CA 93106
AU: Sliter, R W
EM: rsliter@usgs.gov
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025
AB: The regional fault system forming the south boundary of the Western Transverse Ranges Province (WTRP) extends for about 200 km, from near the city of Los Angeles westward along the south flank of the Santa Monica Mountains and through the northern Channel Islands. Multichannel seismic-reflection data show that fault strands within the province-bounding system are active, and some have dip-slip displacements measured in kilometers. The left-oblique Dume fault is active and shows large displacement as far west as Sycamore knoll, but farther west, the fault tip and a superjacent fold are deeply buried. Thus during future earthquakes, the structural transition near the knoll could represent a boundary between earthquake-rupture segments. The east-west province-bounding fault system strikes at a high angle across and terminates the northwest-trending faults, basins and ridges of the California Continental Borderland. Borderland structures considered here form the western limit of intense middle Miocene oblique extension that accompanied rotation of the WTRP. The transition between extended and intact crust lies along the northwest-trending Santa Cruz-Catalina and Santa Rosa-Cortes Ridges. After the Miocene rotation, structures within these ridges became involved in regional transpression, such that northwestward along the Santa Cruz-Catalina Ridge, thrust faulting becomes increasingly more intense, and adjacent to the province boundary, thrust-faulted rocks completely override Miocene extensional structures. In contrast, rocks making up the Santa Rosa-Cortez Ridge are little deformed. The difference in deformation of the two ridges could result from a combination of: 1) eastward crustal thinning and consequent weakening that developed during the Miocene extension; 2) a difference in horizontal strain across the right-slip San Clemente fault near its termination at the WTRP boundary; 3) strain partitioning along this boundary; and 4) a contrast in bulk rheological properties of the ridges.
DE: 8015 Local crustal structure
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8107 Continental neotectonics (8002)
SC: Tectonophysics [T]
MN: Fall Meeting 2005