HR: 13:40h
AN: T42C-01 INVITED     [PDF]
TI: Geodetic and Seismic Constraints on some Seismogenic Zone Processes in Costa Rica
AU: * Dixon, T
EM: tdixon@rsmas.miami.edu
AF: University of Miami, RSMAS, 4600 Rickenbacker Cswy, Miami, FL 33149 United States
AB: E. Norabuena (UM/RSMAS), S. Schwartz and H. DeShon (UCSC) L. Dorman (SIO), E. Flueh (GEOMAR), P. Lundgren (JPL), A. Newman, F. Pollitz (USGS), M. Protti (OVSICORI). We report results from joint seismic (on-land PASCAL and offshore OBS) and geodetic (GPS) observations in Costa Rica designed to elucidate seismogenic zone processes related to subduction of the Cocos plate beneath the western edge of the Caribbean plate. For the Nicoya peninsula, where our seismic deployment was longer, the seismic data are used to constrain the geometry of the plate interface for purposes of modeling the geodetic data. Seismogenic zone events here show significant updip variability, corresponding to changes in subducted oceanic crust origin and heat flow. Inversion of the GPS data here suggests a patchy distribution of locked zones, with two relatively small, elliptically shaped locked zones elongated parallel to the trench (centered on 14 and 38 km depth) within a larger region of low locking (or possibly freely slipping), as well as northeast motion of a coastal "sliver block" at 8 plus/minus 3 mm/yr associated with oblique convergence. In contrast, for the Osa peninsula, there is no evidence of trench-parallel motion (convergence here is orthogonal) and the entire plate interface to a depth of about 50 km appears to be fully locked. In addition, the southwest-dipping block boundary on the Caribbean coast separating the Panama block and Caribbean plate also appears to be fully locked and accumulating strain, with shortening rates of about 1-2 cm/yr. The large zone of locked slip on the main plate interface beneath the Osa Peninsula, as well as the associated "back-arc" deformation, is presumably related to subduction of the shallow Cocos Ridge and consequent high compressive stress in the direction of plate convergence. Over geologic time, this may promote crustal shortening in the region, and uplift of the Cordillera Talamanca in southern Costa Rica.
DE: 1206 Crustal movements--interplate (8155)
DE: 1243 Space geodetic surveys
DE: 3025 Marine seismics (0935)
DE: 7230 Seismicity and seismotectonics
DE: 8102 Continental contractional orogenic belts
SC: Tectonophysics [T]
MN: 2003 Fall Meeting