HR: 1330h
AN: T52B-0261    [PDF]
TI: Shallow Subduction Zone Structure in Northern Costa Rica From Receiver Function Analysis at CRSEIZE Stations
AU: Schwartz, S Y
EM: sschwartz@es.ucsc.edu
AF: Earth Sciences and IGPP, University of California, Santa Cruz, Santa Cruz, CA 95064 United States
AU: * Flores, C
EM: cflores@es.ucsc.edu
AF: Earth Sciences and IGPP, University of California, Santa Cruz, Santa Cruz, CA 95064 United States
AU: DeShon, H R
EM: hdeshon@es.ucsc.edu
AF: Earth Sciences and IGPP, University of California, Santa Cruz, Santa Cruz, CA 95064 United States
AB: CRSEIZE (Costa Rica Seismogenic Zone Experiment) is a collaborative effort to better understand seismogenic behavior at the Costa Rican convergent margin using data from land and ocean bottom seismic networks, oceanic fluid flux meters and GPS receivers. In a continuing effort to refine images of the velocity structure of the subduction margin in this region, receiver function analysis of land and ocean bottom seismic data has been performed, providing information on the depth to and velocity and density contrasts across sharp horizontal discontinuities. Supplementing the CRSEIZE network offshore and across the Nicoya Peninsula with broadband stations of the Arenal Volcano seismic network and Geoscope station JTS, provides station coverage that spans from oceanward of the Middle America Trench to the volcanic arc across northern Costa Rica. Conversions and reflections from two dominant discontinuities are evident in the receiver functions from the Nicoya Peninsula land stations. The depth of these discontinuities increases as the distance between the station and the trench increases, indicating that the discontinuities are likely associated with the subducting oceanic lithosphere. We interpret these reflectors as the boundary between oceanic layer 2 and layer 3 and the oceanic Moho respectively. Thus, we are able to provide constraints on the depth to the subducting slab and details of its velocity structure. Our modeled P-wave velocities for oceanic layer 2 are anomalously low for oceanic crust of 20-25 Ma but are consistent with previous refraction and seismic tomography results. These low velocities possibly suggest a high degree of hydration of the oceanic crust. The degree of hydration of oceanic crust and the fate of the water carried in this crust are not well known but are potentially very important to the processes of earthquake generation and magma genesis. We interpret our receiver functions in conjunction with results of a 3D local tomographic study for the Nicoya Peninsula region in order to better understand the structure and mechanics of the Costa Rican subduction zone.
DE: 7218 Lithosphere and upper mantle
DE: 7220 Oceanic crust
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting