HR: 14:45h
AN: T33E-05    [Abstracts]
TI: Active Crustal Deformation in the Western US: A 3D Finite Element Model
AU: * Yang, Y
EM: yangyo@missouri.edu
AF: University of Missouri-Columbia, 101 Geology, Columbia, MO 65211 United States
AU: Liu, M
EM: lium@missouri.edu
AF: University of Missouri-Columbia, 101 Geology, Columbia, MO 65211 United States
AB: Gravitational potential energy has been suggested as the major cause of the diffuse crustal deformation in the western United States through the late Cenozoic, whereas recent geodesy (mainly GPS) measurements indicate strong influence of plate boundary force on the active deformation. Some studies have also emphasized the role of traction at the base of the lithosphere. We have developed a 3-dimensional finite element model to assess the different roles of these driving forces. The model rheology is that of a temperature-dependent power-law fluid. A series of experiments have been conducted to explore the effects of the various driving forces, the heterogeneity of rheology structure, and the boundary conditions. Major constraints for the model include the strain rate field derived from the GPS data, and stress state in the crust from earthquake data and other data from world stress map. Our results indicate that much of stress patterns in the western US are consistent with the dominance of the gravitational buoyancy forces; the effects of plate boundary forces along the San Andreas fault are largely limited to the region within a couple of hundred kilometers of the plate boundary. The present surface velocity field and stress states can be explained by the combined influences of gravitational buoyancy force and plate boundary force without appealing to basal shear. The model predicts concentration of strain energy in the western Basin and Range province, consistent with high seismicity in this region. Fitting the GPS data from the Cascadian region requires strong coupling between the Juan de Fuca plate and North America. With the timescale-dependent crustal rheology, the model predicts short-term (interseismic) NE-SW shortening as shown by the GPS data, and long-term N-S compression in the northwestern Pacific region consistent with earthquake data.
UR: http://www.geongrid.org
DE: 9350 North America
DE: 9604 Cenozoic
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting