HR: 0800h
AN: S31A-0203    [Abstracts]
TI: Determining Three Dimension Q – Attenuation Structure beneath Kyushu Island, Japan exerting Waveform – Spectra of Microearthquakes
AU: * Parithusta, R
EM: rizkita@sevo.kyushu-u.ac.jp
AF: Department Planet and earth sciences, Graduates School of Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka, 8128561, Japan
AU: Matsumoto, S
EM: matumoto@sevo.kyushu-u.ac.jp
AF: Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 2-5643-29 Shin'yama Shimabara, Nagasaki, 8550843, Japan
AU: Shimizu, H
EM: shimizu@sevo.kyushu-u.ac.jp
AF: Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 2-5643-29 Shin'yama Shimabara, Nagasaki, 8550843, Japan
AB: Examining the anelastic structure in the uppermost mantle and the crust continues to be a significant problem in seismology. In particular, the observation of attenuation heterogeneities around subduction zones and active fault has implication for the dynamic oceanic lithosphere and asthenosphere. Seismic attenuation can be estimated by extracting the amplitude-frequency information contained in seismic waveforms and it provides an important insight into the nature of heterogeneities structure and composition of the earth's interior. The study area at Kyushu Island, in South Part of Japan is characterized by subduction from Philippine Sea Slab and Eurasian Plate; volcanic front seen in islands arcs runs through the central part of Kyushu Island. Futagawa- Hinagu Fault zone, which is one of the active faults in Japan, lies in the middle of Kyushu, in which the seismic activity of shallow earthquakes is high. The fault is furrow from southwest of Aso volcano until Yatsushiro city, with the type of right-lateral strike slip. For investigating the 3D wave attenuation Q structure of the crust and the upper mantle in Kyushu Island, we examined the seismic wave spectra for micro earthquakes (Magnitude 2.5 – 4.5) observed at seismic stations by Kyushu Univ., JMA, and Hi-net. In this study selected waveform were used for spectral analysis concerning strong lateral heterogeneities, to estimate Q values by the spectral decay of the spectrum. Used for estimating path attenuation, we obtained the best result with amplitude spectra determined for a 128 - sample window around seismic-wave arrivals and having signal-to-noise ratio greater than 2 over the continuous frequency range. Solving for Q structure, an inversion program were developed with referring Tsumura, 2000.,by given a set of path attenuation, source parameter, site response and velocity model, the Q structure can be distinguished the difference between fore-arc zone and back arc zone around Kyushu Island, especially from the Philippine Sea Slab (subduction). A record of an event distance from the network suggested that high attenuation (Low-Q) was exposed under volcanic areas (in the crust and mantle wedge) along the central of Kyushu Island, and for low attenuation (High- Q) was showing the figure of subducting Philippine Sea Slab. The variations in seismic attenuation can be attributed to a high attenuation (low-Q) zone in the mantle underneath the volcanic area of Kyushu Area; it was formalize by performing the Q structure inversion. Keywords: Attenuation, Q, 3-D structure, Kyushu Island
DE: 7200 SEISMOLOGY
DE: 7205 Continental crust (1219)
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: 2007 Fall Meeting