HR: 0800h
AN: T11D-1296    [Abstracts]
TI: Testing 3D fault configuration in the northern Los Angeles basin, California via patterns of rock uplift the since 2.9 Ma
AU: * Cooke, M
EM: cooke@geo.umass.edu
AF: Department Geosciences, 611 North Pleasant St University of Massachusetts, Amherst, MA 01003-9207 United States
AU: Meigs, A
EM: meigsa@geo.oregonstate.edu
AF: Department Geosciences, 104 Wilkinson Hall Oregon State University, Corvallis, OR 97331 United States
AU: Marshall, S
AF: Department Geosciences, 611 North Pleasant St University of Massachusetts, Amherst, MA 01003-9207 United States
AB: Competing models of three-dimensional fault topology, starting from the Southern California Earthquake Center (SCEC) Community Fault Model (CFM), were tested for viability using numerical Boundary Element Method (BEM) models and patterns of rock uplift by folds in the northern Los Angeles basin Los Angeles basin. Thirteen structural cross-sections constrained by well and outcrop data were used to compile a structure contour map of the base of the Pico Formation (2.9 Ma) across about 50 km of the northern Los Angeles basin from the Coyote Hills on the east to Pacific Palisades on the west. A map of rock uplift rate was constructed from these data by measuring the structural relief relative to the central trough of the Los Angeles basin, a long-lived northwest-trending structural low that lies to the northeast of the Newport-Inglewood fault. BEM models of 3D fault topology were used to generate uplift rates over the same region using North-South contraction at 100 nanostrain/year. A suite of models investigate the sensitivity of uplift patterns to 1) dip of blind thrust faults (e.g. Las Cienegas and Elysian Park), 2) presence of low-angle (20 degree) thrust ramp below 10 km depths 3) regional extent of this low-angle ramp and 4) inclusion of near surface splays of the Santa Monica fault. Model-data compatibility was evaluated on the basis of structural trend, spatial variation in rates and location of major structures (i.e. key near surface folds). All models are consistent with the location and uplift pattern of the Coyote Hills and Santa Fe Springs structures, the location and orientation of the central trough, and a North-trending structure separating Santa Fe Springs on the east from Montebello to the northwest. Incorporation of the low-angle ramp below 10 km depth that is regionally extensive (i.e. many faults sole into this fault) improves model and geologic uplift compatibility. Furthermore, steepening the Las Cienegas and Elysian Park faults to 60 degrees reduces mismatch. If correct, our models are consistent with the emerging paradigms that 1) the north and northeastern boundaries of the Los Angeles basin's central trough are flanked by deep (> 10 km) and low-angle ($<$30 degree) fault ramps and 2) near surface thrust faults merge into this ramp with steep (60 degree) dips.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8107 Continental neotectonics
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting