HR: 0800h
AN: T21C-0504    [Abstracts]
TI: Comparison of GPS Data From the Ventura Basin, California to Interseismic Three-Dimensional Mechanical Models
AU: * Marshall, S T
EM: marshall@geo.umass.edu
AF: University of Massachusetts, 611 North Pleasant St., Amherst, MA 01003-9207 United States
AU: Cooke, M L
EM: cooke@geo.umass.edu
AF: University of Massachusetts, 611 North Pleasant St., Amherst, MA 01003-9207 United States
AU: Owen, S
EM: owen@terra.usc.edu
AF: University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089 United States
AB: Geodetic data from the Southern California Integrated Geodetic Network (SCIGN) provide information on interseismic deformation patterns in the Ventura Basin, which can be compared to results from three-dimensional mechanical models. This comparison may determine the most realistic among differing three-dimensional active fault configurations and predict slip rates for unconstrained faults. Although the Ventura basin is one of the fastest converging areas within southern California, geodetic signals are complicated by seasonal fluid injection/withdrawal. We use geodetic data that has been corrected for seasonal anthropomorphic effects for comparison to a set of three-dimensional mechanical models. For our models, we use three-dimensional triangulated fault surfaces defined by the Community Fault Model (CFM) for the Ventura Basin. Fault surfaces from the CFM have been modified to extend below the seismogenic portion of the crust (depth < 18 km) to a 27 km deep freely-slipping horizontal crack representing the Mohorovic Discontinuity. We establish two sets of Boundary Element Method (BEM) models, one with 149›¦ remote contraction determined from relative displacement of distal SCIGN stations and one with N-S contraction, similar to tectonic boundary conditions of the nearby Los Angeles basin. For each set of tectonic boundary conditions, we calculate fault slip rates over a simulated period of 5000 years, which should exceed the recurrence intervals for all faults. Within each model, the greater compliance of the 6 km deep sedimentary basin, relative to the surrounding basement, is simulated by a network of small randomly oriented cracks. The density and length of cracks is chosen to approximate the stiffness of sedimentary material under the applied strain rates. For validation of the three-dimensional model and tectonic boundary conditions, fault slip rates and rakes are calculated and are compared to available paleoseismic rates. Our results suggest that model-calculated dip-slip rates are generally within the range of published paleoseismic rates for both tectonic contraction directions tested. Strike-slip rates are more sensitive than dip slip to convergence direction. We simulate interseismic deformation by locking all fault surfaces above 18 km depth and prescribing the slip rates from the best-fitting geologic slip model to the portions of fault surfaces that fall below the 18 km seismogenic locking depth. Model surface velocities are compared to geodetic data. We observe that the modeled interseismic deformation patterns resemble that of the geodetic data. Furthermore, the sensitivity of fault slip rates and surface velocities to amplitude of fault surface topology are assessed by comparison to a model with simple planar faults.
DE: 8100 TECTONOPHYSICS
DE: 8108 Continental tectonics: compressional
DE: 8109 Continental tectonics: extensional (0905)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: Fall Meeting 2005