HR: 0800h
AN: S51B-0154    [Abstracts]
TI: Intermediate depth seismicity - a reflection seismic approach
AU: Haberland, C
EM: haber@geo.uni-potsdam.de
AF: University of Potsdam, Institute of Geosciences, P.O. Box 60 15 53, Potsdam, 14415 Germany
AU: * Rietbrock, A
EM: A.Rietbrock@liv.ac.uk
AF: The University of Liverpool, Department of Earth and Ocean Sciences, 4 Brownlow Street, Liverpool, L69 3GP United Kingdom
AB: During subduction the descending oceanic lithosphere is subject to metamorphic reactions, some of them associated with the release of fluids. It is now widely accepted, that these reactions and associated dehydration processes are directly related with the generation of intermediate depth earthquakes (dehydration embrittlement). However, the structure of the layered oceanic plate at depth and the location of the earthquakes relative to structural units of the subducting plate (sources within the oceanic crust and/or in the upper oceanic mantle lithosphere?) are still not resolved yet. This is in mainly due to the fact that the observational resolution needed to address these topics (in the range of only a few kilometers) is hardly achieved in field experiments and related studies. Here we study the wavefields of intermediate depth earthquakes typically observed by temporary networks in order to assess their high-resolution potential in resolving structure of the down going slab and locus of seismicity. In particular we study whether the subducted oceanic Moho can be detected by the analysis of secondary phases of local earthquakes (near vertical reflection). Due to the irregular geometry of sources and receivers we apply an imaging technique similar to diffraction stack migration. The method is tested using synthetic data both based on 2-D finite difference simulations and 3-D kinematic ray tracing. The accuracy of the hypocenter location and onset times crucial for the successful application of stacking techniques (coherency) was achieved by the use of relatively relocated intermediate depth seismicity. Additionally, we simulate the propagation of the wavefields at larger distance (wide angle) indicating the development of guided waves traveling in the low-velocity waveguide associated with the modeled oceanic crust. We also present application on local earthquake data from the South American subduction zone.
DE: 9360 South America
DE: 7230 Seismicity and seismotectonics
DE: 8105 Continental margins and sedimentary basins
DE: 7203 Body wave propagation
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting