HR: 16:45h
AN: T54A-04    [Abstracts]
TI: Waveform Modeling Of The Slab In Japan Subduction Zone
AU: * Chen, M
EM: mchen@gps.caltech.edu
AF: Seismolab, Caltech, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Tromp, J
EM: jtromp@gps.caltech.edu
AF: Seismolab, Caltech, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Helmberger, D
EM: helm@gps.caltech.edu
AF: Seismolab, Caltech, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Kanamori, H
EM: hiroo@gps.caltech.edu
AF: Seismolab, Caltech, 252-21, Caltech, Pasadena, CA 91125 United States
AB: The P-wave tomographic model derived by Zhao et. al. (1994) for Japan subduction zone has two very striking features : a well-developed slab about 90 km thick with P-wave velocities 3 - 6% higher than the normal mantle, and a mantle wedge with low-velocity anomalies up to - 6%. In order to understand how the slab affects body-wave propagation and infer slab structure from waveform data, we study detailed 3-component seismograms from > 600 Hinet stations produced by two earthquakes (depth > 400 km), which have very simple sources and occurred in the down-going Pacific Plate. We simulate the body-wave propagation in the 3-D P-wave model using 2-D finite-difference (FD) and 3-D spectral-element (SEM) methods. As measured by cross-correlation between synthetics and data, Zhao's P-wave model predicts the data better in terms of both timing and waveform complexity compared to a 1D model. But discrepancies do exist, especially regarding SH-wave waveform distortions. In this study, we take advantage of the densely distributed Hinet stations, and use 2D waveform modeling to simulate the SH waveforms. The resolved 2D vertical model suggests there is a thin, elongated low-velocity layer above the slab about 20 km thick, extending down to a depth of 300 km, with S-wave velocity reduction of 14% compared to the normal mantle. This feature models a strong secondary arrival which is not easily imaged in tomographic methodologies. Such a deep low-velocity layer could explain the relatively weak coupling associated with most subduction zones, which involves with silent earthquakes and volcanic activity.
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005