HR: 12:05h
AN: G12A-08    [Abstracts]
TI: Toward an Improved Understanding of Subduction Zone Mechanics: Finite Element Modeling Results From the Jalisco GPS Project, 1993-2004
AU: * Schmitt, S V
EM: stuart@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI 53706 United States
AU: DeMets, C
EM: chuck@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI 53706 United States
AU: Stock, J
AF: Seismological Laboratory, California Institute of Technology, 1200 E. California Blvd., MS 252-21, Pasadena, CA 91125 United States
AU: Sanchez, O
AF: Instituto de Geofisica, Universidad Nacional Aut\'{o}noma de M\'{e}xico, Ciudad Universitaria, Del Coyoac\'{a}n, M\'{e}xico, DF 04510 Mexico
AU: Masterlark, T
AF: USGS/EROS Data Center, 47914 252nd St., Sioux Falls, SD 57005 United States
AU: Marquez-Azua, B
AF: Departamento de Geografia y Ordenaci\'{o}n Territorial, Universidad de Guadalajara, Av. de los Maestros y Mariano Barcena, Planta Alta, Guadalajara, Jal 44260 Mexico
AB: We use continuous and periodic measurements from a 30-station GPS network along the Pacific coast of western Mexico, adjacent to the subducting Rivera plate, to derive new constraints on subduction mechanics. Two megathrust earthquakes have ruptured the Rivera plate subduction interface immediately offshore from our network since we began measurements in the mid-1990s, the 9 October 1995 M=8.0 Colima-Jalisco earthquake and the 21 January 2003 M=7.6 Tecom\'{a}n earthquake. Continuous GPS measurements after the 1995 earthquake reveal a strong postseismic response in which both the rate and direction evolve through time. Models that attribute the response solely to fault afterslip or postseismic viscoelastic flow fit the observations poorly, independent of the viscosities employed to model the latter response. Motion is instead well fit by a model that superimposes the effects of fault afterslip, viscoelastic flow, and relocking of shallow areas of the subduction interface. Possible triggering of the 2003 earthquake via coseismic and postseismic loading associated with the 1995 earthquake is examined via Coulomb stress analysis. We further present modeling of the unusual GPS displacement field associated with the 2003 earthquake, including the possibility that the earthquake triggered slip, possibly aseismic, along a fault in the upper crust.
DE: 8150 Plate boundary--general (3040)
DE: 8164 Stresses--crust and lithosphere
DE: 1206 Crustal movements--interplate (8155)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting