HR: 0800h
AN: S51B-0157    [Abstracts]
TI: Seismogenic zone structure along the Middle America Trench, Nicoya Peninsula, Costa Rica, from 3D local earthquake tomography
AU: * DeShon, H R
EM: hdeshon@es.ucsc.edu
AF: Earth Sciences Department & IGPP, Univ. of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Schwartz, S Y
EM: susan@es.ucsc.edu
AF: Earth Sciences Department & IGPP, Univ. of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Dorman, L M
EM: ldorman@ucsd.edu
AF: Scripps Institution of Oceanography, Univ. of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093 United States
AU: Newman, A V
EM: anewman@lanl.gov
AF: Los Alamos National Laboratory, EES-9, MS D462, Los Alamos, NM 87545 United States
AU: Protti, M
EM: jprotti@una.ac.cr
AF: Observatorio Vulcanol\'{o}gico y Sismol\'{o}gico de Costa Rica, Universidad Nacional, Apdo. 2346-3000, Heredia, 3000 Costa Rica
AU: Gonzalez, V
EM: vgonzale@una.ac.cr
AF: Observatorio Vulcanol\'{o}gico y Sismol\'{o}gico de Costa Rica, Universidad Nacional, Apdo. 2346-3000, Heredia, 3000 Costa Rica
AB: The shallow seismogenic portion of the Nicoya Peninsula, Costa Rica, segment of the Middle America Trench generates damaging large (M$_{W}$$>$7.5) earthquakes over a recurrence interval of 50 years. We present hypocenters and three-dimensional seismic velocity models ({\it V$_{P}$} and {\it V$_{P}$}/{\it V$_{S}$}) calculated using simultaneous inversion of {\it P}- and {\it S}-wave arrival time data from 611 small magnitude earthquakes. We design a characteristic velocity model using the Nicoya experiment geometry to provide additional resolution estimates. Data was collected as part of the Costa Rica Seismogenic Zone Experiment (CRSEIZE), a collaborative geodetic, passive seismic, and fluid flux program. Along the southern Nicoya Peninsula plate interface microseismicity extends from 12-26 km below sea level ($\sim$73-100 km from the trench axis). To the north interplate seismicity extends from 17-28 km below sea level (75-87 km from the trench axis). Interplate seismicity begins downdip of a shallow geodetically locked patch and region of low {\it V$_{P}$} along the plate interface. The $\sim$5 km depth offset to the updip limit of microseismicity occurs across the plate suture of East Pacific Rise-derived and Cocos-Nazca Spreading Center-derived oceanic lithosphere and correlates with models of the $250\deg$C isotherm; the offset most likely reflects differing thermal regimes of the incoming oceanic crust due to along-strike variations in hydrothermal circulation. The downdip edge of plate interface seismicity occurs updip of the continental Moho/oceanic slab intersection and does not uniquely correlate with models of the $350\deg$C isotherm. Low forearc mantle wedge {\it P}-wave velocities suggest 20-30% serpentinization along the Nicoya Peninsula region; {\it V$_{P}$}/{\it V$_{S}$} ranges from 1.70-1.82 km/sec, values consistent with 0-10% serpentinization.
DE: 8180 Tomography
DE: 7230 Seismicity and seismotectonics
DE: 7260 Theory and modeling
DE: 8105 Continental margins and sedimentary basins
DE: 8123 Dynamics, seismotectonics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting