HR: 1340h
AN: S53B-0201    [Abstracts]
TI: Implications of Seismic Waveforms: Complex Physical Properties Associated with Stagnant Slab
AU: * TAJIMA, F
EM: fumiko@geol.sci.hiroshima-u.ac.jp
AF: Hiroshima University, Graduate School of Science, Kagamiyama 1-3-1, Higashi Hiroshima, 739-8526 Japan
AU: NAKAGAWA, T
EM: nakagawa@geol.sci.hiroshima-u.ac.jp
AF: Hiroshima University, Graduate School of Science, Kagamiyama 1-3-1, Higashi Hiroshima, 739-8526 Japan
AB: Regional broadband waveform modeling can elaborate the structure in the areas where seismic tomography studies captured the bulk of high velocity anomaly (HVA) in the upper mantle transition zone. Our recent study shows that P-wave velocity model M3.11 or M2.0, if not iasp91, generally explains regional waves that strongly sampled the transition zone in the northwestern Pacific subduction zones (Tajima and Grand, 1995, 1998). Here M3.11 is consistent with the thermo-chemical condition of a deflected cold slab in the transition zone, and explains the structure in the southern Kuriles to northeastern Japan subduction zones. M2.0 has HVA in the deeper part of the transition zone without broad depression of the 660 km discontinuity, and explains the structure beneath the northern most Philippine Sea Plate. It is noted, however, some waves observed for deep focus events whose source processes are basically simple, show substantial broadening after the direct P arrivals and were not modeled by either of these models. The sampling rays of these data are not very different from those whose waveforms were used to derive M3.11 or M2.0. The waveform broadening probably indicates excitations of reflected, refracted or converted waves at the velocity heterogeneities associated with the slab. Whether the heterogeneities are located around the slab boundaries or involve in the chemical composition within the slab such as metastable phases has not been determined yet as the present data sampling is not dense enough to draw definite conclusions. However, we show how sensitive regional seismic body waves are to the structure associated with stagnant slab, and present some models that were tested for the causes of waveform broadening.
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
DE: 1645 Solid Earth
SC: Seismology [S]
MN: 2004 AGU Fall Meeting