HR: 1340h
AN: T33A-1334    [Abstracts]
TI: On Resolution of Surface Wave Tomography: Geometrical Rays and Finite-Width Rays
AU: * YOSHIZAWA, K
EM: kazu@belinda.ep.sci.hokudai.ac.jp
AF: Division of Earth and Planetary Sciences, Hokkaido University, Sapporo, 060-0810 Japan
AU: KENNETT, B L
EM: brian@rses.anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AB: Recent developments of finite-frequency sensitivity kernels for surface waves enable us to perform forward and inverse modeling taking account of the effects of scattering and diffraction of surface waves. We have recently developed a three-stage inversion technique to obtain regional surface wave tomography incorporating finite frequency effects utilizing the "influence zone", which can be represented as approximately one-third of the width of the first Fresnel zone (Yoshizawa and Kennett, 2002 GJI). The method has been applied to the Australian region (Yoshizawa and Kennett, 2004 JGR) and to the Philippine Sea region (Isse et al., 2004, AGU Fall Meeting). In this study we perform synthetic experiments, using the influence zone kernels, to assess the intrinsic differences in the resolutions of tomography models with or without the effects of finite frequency. The results of checker board resolution tests indicate improved resolution of finite frequency models; i.e., we can recover both the amplitude and patterns of lateral heterogeneity at scales of a few hundred kilometers quite well. Although large-scale heterogeneity patterns with scale length over 500 km can be retrieved well by both ray theory and finite-frequency theory, some artificial patch-like features tend to contaminate the ray-theoretical models, especially in regions with low path density. The variance reductions achieved by finite-frequency models for the Australian region are nearly 10% higher than those achieved by the ray-theoretical models. The main differences arise from different spatial sensitivities between ray-theoretical and finite-frequency kernels. In the ray theory, the along-path sensitivity is always constant. On the contrary, the finite-frequency kernels have conspicuous peaks of sensitivity near the source and receiver locations, which results in better resolutions in regions with higher sensitivity. Such effects are apparent in the actual tomography models in the Australian region, i.e., clearer images of subducting plates can be seen in the New Hebrides and Tonga-Kermadec.
DE: 8180 Tomography
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7218 Lithosphere and upper mantle
DE: 1213 Earth's interior--dynamics (8115, 8120)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting