HR: 0800h
AN: S51A-0981    [Abstracts]
TI: Spatial Distribution of Medium Heterogeneity Beneath Eurasian Continent and Western Pacific as Revealed From Teleseismic P-coda
AU: * Kubanza, M
EM: kubanza@zisin.geophys.tohoku.ac.jp
AF: Graduate school of science, Tohoku University, Sendai, 980-8578 Japan
AU: Nishimura, T
EM: nishi@zisin.geophys.tohoku.ac.jp
AF: Graduate school of science, Tohoku University, Sendai, 980-8578 Japan
AU: Sato, H
EM: sato@zisin.geophys.tohoku.ac.jp
AF: Graduate school of science, Tohoku University, Sendai, 980-8578 Japan
AB: We systematically characterize the heterogeneous structure of the lithosphere by analyzing transverse amplitude of teleseismic P-coda, since the transverse components of P-wave are generated from lateral heterogeneity of the structure. We use 1619 bandpass filtered seismograms (0.5-1, 1-2 and 2-4 Hz) of deep and shallow events recorded at IRIS GSN stations. For each event-station pair, we calculate the energy partition of P-coda waves into the transverse component, and then we take its root-mean-square amplitude that represents normalized transverse amplitude. We further average the transverse amplitudes from deep and shallow events, respectively, at each station. We call this average transverse amplitude. The results show a clear positive correlation between the average transverse amplitude from deep events and those from shallow ones for all of the stations where both events are observed. This result strongly suggests that the average transverse amplitude estimated from shallow events can be used to characterize the heterogeneity of the lithosphere beneath the stations. That is, we are able to characterize the medium heterogeneity in wide area because shallow events are well recorded at many stations around the world. The observed average transverse amplitudes of shallow events show significant regional difference of heterogeneity that relate to tectonic conditions. Most of large average transverse amplitudes are observed at stations located on active tectonic regions along the collision zones in the southern Eurasia and the subduction zones in the western Pacific. A polar station located on the north Atlantic ridge-transform system also indicates large average transverse amplitude. The mid Eurasia and Australia, which are tectonically quiet regions on stable continents, show small average transverse amplitude. We further compare the average transverse amplitudes with the number of earthquakes within 300 km distance from each station for the past 30 years. The results show that seismically active regions are always characterized by large amplitudes. However large average transverse amplitudes do not always indicate high seismicity. This implies that the average transverse amplitudes detect medium heterogeneity that does not relate with current seismicity.
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005