HR: 0800h
AN: T21C-0545    [Abstracts]
TI: Long Term Seismic Observation in Mariana by OBSs : Results of the DD inversion
AU: * Shiobara, H
EM: shio@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032 Japan
AU: Sugioka, H
EM: hikari@jamstec.go.jp
AF: IFREE, Jamstec, Natsushima 2-15, Yokosuka, 237-0061 Japan
AU: Mochizuki, K
EM: kimi@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032 Japan
AU: Oki, S
EM: toko@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032 Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032 Japan
AU: Fukao, Y
EM: fukao@jamstec.go.jp
AF: IFREE, Jamstec, Natsushima 2-15, Yokosuka, 237-0061 Japan
AU: Suyehiro, K
EM: suyehiro@jamstec.go.jp
AF: Jamstec, Natsushima 2-15, Yokosuka, 237-0061 Japan
AB: In order to obtain the deep arc structural image of Mariana, a large-scale seismic observation by using 58 long-term ocean bottom seismometers (LTOBS) had been performed from June 2003 until April 2004, which is a part of the MARGINS program funded by the NSF. Prior to this observation, a pilot long-term seismic array observation was conducted in the same area by using 10 LTOBSs from Oct. 2001 until Feb. 2003. By using seven LTOBS's data, those are about 11 months long, hypocenter determination was performed at first and more than 3000 local events were found, although the PDE list contains only 59. A 1D velocity structure based on the iasp91 model was used, and a systematic shift of epicenters between the PDE list and this study was seen. To investigate the detail of hypocenter distribution and the 3D velocity structure, the DD inversion (tomoDD: Zhang and Thurber, 2003) was applied for this data set with a 1D structure initial model except for the crust, which has been surveyed by using a dense airgun-OBS system (Takahashi et al., 2003). The result of relocated hypocenters shows double seismic zones until about 200km depth and a lined focuses along the current ridge axis in the back-arc basin, and the result of the tomographic inversion shows a image of subducting slab and a low-Vs region below the Pagan island erupted in 1981 at 80km depth. The mantle structure beneath the back-arc basin was not clearly resolved due to the inadequate source-receiver coverage, which is cleared in the recent experiment.
DE: 8180 Tomography
DE: 7230 Seismicity and seismotectonics
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting