HR: 09:30h
AN: S11D-05    [Abstracts]
TI: Guided Waves in Subduction Zones and the Heterogeneity Structure of the Subducted Plate
AU: Furumura, T
EM: furumura@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-Ku, Tokyo, 113-0032 Japan
AU: * Kennett, B L
EM: Brian.Kennett@anu.edu.au
AF: Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200 Australia
AB: Sharp shocks of high intensity are frequently observed on the eastern seaboard of Japan from deep earthquakes in the Pacific plate. The recordings of such events at stations in the region of high intensity show a low-frequency (< 0.5 Hz) onset for both P and S waves followed by large, high-frequency (> 2 Hz) later arrivals with a long coda. This behavior is not explained by a subduction zone model comprising a just high velocity plate with low attenuation. From the analysis of observed broadband waveforms and numerical simulation of seismic wave propagation in 2-D and 3-D models we demonstrate that the high-frequency guided waves traveling in the subducting plate arise from the scattering of seismic waves by heterogeneity within the plate. Our preferred model of the heterogeneity has elongated scatterers parallel to the plate margin described by a von Karmann function with a down-dip correlation length of about 10 km and much shorter correlation length of about 0.5 km in thickness. The standard deviation of wavespeed fluctuations from the averaged background model is about 2 percent. This new plate model produces the required frequency-selective propagation characteristics through scattering of the high-frequency components. Three-dimensional simulations of the expected propagation characteristics for a deep earthquakes recorded in northern Japan for a realistic plate model display anomalously large intensities and distorted intensity patterns comparable to observed patterns. The simulations employ parallel computation on the Earth Simulator supercomputer with a high-resolution structural model including stochastic heterogeneity in the subducted plate. The simulations demonstrate clearly the scattering waveguide effects for high-frequency waves.
DE: 7260 Theory and modeling
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting