HR: 0830h
AN: T51D-0187    [PDF]
TI: Using Three-dimensional Mechanical Models of the Los Angeles Basin, California, to Validate Tectonic Boundary Conditions and Locate Unrecognized Secondary Faults
AU: * Griffith, W A
EM: wagrif@geo.umass.edu
AF: Stanford University, Dept. of Geological and Environmental Sciences 450 Serra Mall Braun Hall, Building 320, Stanford, CA 94305-2115 United States
AU: Cooke, M L
EM: cooke@geo.umass.edu
AF: University of Massachusetts, Department of Geoseciences 233 Morrill Science Center 611 North Pleasant St, Amherst, MA 01003-9297 United States
AB: Geodetic studies have calculated horizontal strain rates that represent different degrees of vertical thickening vs. escape tectonics in the Los Angeles basin. In this study, three-dimensional mechanical models are used to compare fault slip rates resulting from four representative tectonic boundary conditions for this region to paleoseismic and geologic late-Quaternary slip rates. Resulting best-fit tectonic boundary conditions are applied to the model to identify potential locations of unrecognized secondary faults in the eastern Los Angeles basin. We conclude that north-south contraction in the basin is accompanied by negligible east-west strain, suggesting a vertical thickening, rather than escape tectonics scenario. Under the preferred tectonic boundary conditions, the pattern of strain energy density (SED) of host rock highlights potential areas of unrecognized faulting, and the Navier-Coulomb stress criterion predicts the orientation of potential failure planes at these locations. The non-uniform distribution of SED throughout the model suggests: 1) clustering of secondary faults near intersecting major faults (e.g. hanging wall of the Puente Hills thrusts); 2) linkage of proximal faults (e.g. Whittier and Alhambra Walsh faults); and 3) extension of some fault surfaces (e.g. Chino and Compton faults). Correspondingly, the Navier-Coulomb stress in these locations predicts that fault plane orientations are influenced by the geometry of existing faults rather than by tectonic boundary conditions. Additionally, whereas some areas of low fault density have high SED (e.g. south of the Cucamonga fault), others do not. Moreover, the location and orientation of the proposed Montebello fault predicted by the model results matches that inferred from surface geology.
UR: http://www.geo.umass.edu/faculty/cooke/topics/LA.html
DE: 1206 Crustal movements--interplate (8155)
DE: 7215 Earthquake parameters
DE: 8010 Fractures and faults
DE: 8020 Mechanics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting