HR: 11:20h
AN: T41E-05    [PDF]
TI: Geometry and velocity structure of the northern Costa Rica seismogenic zone from 3D local earthquake tomography
AU: * DeShon, H R
EM: hdeshon@es.ucsc.edu
AF: Earth Sciences Dept. \& IGPP, UCSC, 1156 High St., Santa Cruz, CA 95062
AU: Schwartz, S Y
EM: susan@es.ucsc.edu
AF: Earth Sciences Dept. \& IGPP, UCSC, 1156 High St., Santa Cruz, CA 95062
AU: Newman, A V
AF: Los Alamos National Laboratory, EES-9, MS D462, Los Alamos, NM 87545
AU: Dorman, L M
AF: Scripps Institute of Oceanography, UCSD, 9500 Gilman Drive, La Jolla, CA 92093
AU: Protti, M
AF: OVSICORI-UNA, Apdo. 2346-3000, Heredia, 3000 Costa Rica
AU: Gonzalez, V
AF: OVSICORI-UNA, Apdo. 2346-3000, Heredia, 3000 Costa Rica
AB: We present results of a 3D local earthquake tomography study of the Middle America Trench seismogenic zone in northern Costa Rica. Local earthquake tomography can provide constraints on the updip, downdip, and lateral variability of seismicity and P- and S-wave velocities; these constraints may in turn provide information on compositional and/or mechanical variability along the seismogenic zone. We use arrival time data recorded by the Nicoya Peninsula seismic array, part of the Costa Rica seismogenic zone experiment (CRSEIZE), a collaborative effort undertaken to better understand seismogenic behavior at the Costa Rica subduction zone using data from land and ocean bottom seismic arrays, oceanic fluid flux meters, and GPS receivers. We invert $\sim$10,000 P-wave and S-wave arrival times from 475 well-recorded local earthquakes (GAP $<$ $180\deg$, $>$8 P-wave arrivals) to solve for the best-fitting 1D P- and S-wave velocity models, station corrections, and hypocenters using the algorithm VELEST. These 1D velocity models are used as a starting models for 3D simultaneous inversion using the algorithm SIMULPS14. Preliminary P-wave inversions contain a positive velocity anomaly dipping beneath the Nicoya Peninsula, interpreted as the subducting Cocos Plate. Earthquakes occur in a narrow band along the slab-continent interface and are consistent with the results of {\it Newman et al.} (2002). The updip limit of seismicity occurs $\sim$5 km deeper and 5-10 km landward in the northern vs. the southern Nicoya Peninsula, and this shift spatially correlates to the change from Cocos-Nazca to East Pacific Rise derived oceanic plate. P-wave velocities in the upper 5-10 km of the model are consistent with the geology of the Nicoya Peninsula. We will correlate relocated microseismicity to previously noted variability in oceanic plate morphology, heat flow, fluid flow, and thermal structure and compare the resulting P- and S-wave velocity models to wide-angle refraction models and hypothesized mantle wedge compositions.
DE: 7209 Earthquake dynamics and mechanics
DE: 7230 Seismicity and seismotectonics
DE: 7299 General or miscellaneous
DE: 8105 Continental margins and sedimentary basins
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting