HR: 15:10h
AN: S43D-07    [Abstracts]
TI: Large-scale Seismic and Aseismic Deformation Patterns Associated With Subduction: Constraints From Continuous GPS measurements in Mexico
AU: DeMets, C
EM: chuck@geology.wisc.edu
AF: University of Wisconsin, Department of Geology and Geophysics, Madison, WI 53706 United States
AU: * Brudzinski, M R
EM: brudzins@geology.wisc.edu
AF: University of Wisconsin, Department of Geology and Geophysics, Madison, WI 53706 United States
AU: * Brudzinski, M R
EM: brudzins@geology.wisc.edu
AF: Miami University, Department of Geology, Oxford, OH 45056 United States
AU: Cabral-Cano, E
EM: ecabral@tonatiuh.igeofcu.unam.mx
AF: Universidad Nacional Aut\'{o}noma de M\'{e}xico, Instituto de Geof\'{i}sica, Mexico City, 04510 Mexico
AU: M\'{a}rquez-Az\'{u}a, B
EM: bmarquez@udgserv.cencar.udg.mx
AF: Universidad de Guadalajara, Departamento de Geograf\'{i}a y Ordenaci\'{o}n Territorial, Guadalajara, 44600 Mexico
AU: Correa-Mora, F
EM: fcorrea@geology.wisc.edu
AF: University of Wisconsin, Department of Geology and Geophysics, Madison, WI 53706 United States
AU: Correa-Mora, F
EM: fcorrea@geology.wisc.edu
AF: Universidad Nacional Aut\'{o}noma de M\'{e}xico, Instituto de Geof\'{i}sica, Mexico City, 04510 Mexico
AB: We use coordinate time series from 27 continuous GPS stations in Mexico, including five new sites, to describe evidence for seismic and aseismic slip along the Middle America subduction interface. Spatial filtering of our GPS coordinate time series effectively removes inter-site correlated noise from external, non-tectonic causes, precluding them as an explanation for the movements we observe. For the 1995 M$_{W}$ = 8 Colima-Jalisco megathrust earthquake, we find previously undescribed displacements of up to 20 millimeters during and after the earthquake at sites up to 400 km from the epicenter. Periods of aseismic transient slip, some previously unrecognized, are apparent in the time series for GPS stations along most of the Pacific coast and up to 500 km inboard from the trench. Between early 1993 and early 2004, we recognize episodes of transient strain release late in 1995 and early in 1998, 1999, 2000, 2001 and 2002. In each event, over 10 millimeters of transient slip was recorded by at least three stations within two months of one another, and all of these sites are found to be moving toward the Middle America trench during the transients, consistent with protracted relaxation of elastic strain related to subduction. We estimate the onset, duration, magnitude, and direction of transient displacement by a least-squares inversion to find the best fit hyperbolic tangent functions describing the GPS coordinate time series. Considering that many sites moved coherently towards an area between Acapulco and Oaxaca, we also employ an inverse procedure to examine whether transients observed within the network are consistent with a source of slip that is stationary or propagating. In either case, our results underscore the importance of transient aseismic fault slip in accommodating subduction. Given our evidence for coordinated transient signals at sites far from the trench, our results demonstrate the geographically extensive effects of this phenomenon in Mexico, presumably due to the shallow subduction angle of the Cocos plate. These results imply that future geodetic tests for crustal deformation within Mexico must consider the complicating effects of transient slip on the motions of sites far from the trench.
DE: 8123 Dynamics, seismotectonics
DE: 8158 Plate motions--present and recent (3040)
DE: 7209 Earthquake dynamics and mechanics
DE: 1206 Crustal movements--interplate (8155)
DE: 1242 Seismic deformations (7205)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting