HR: 0800h
AN: T21C-0506    [Abstracts]
TI: Mantle wedge structure beneath an eastern part of the Japan Sea revealed by long-term broadband seafloor seismic observation
AU: * Nakahigashi, K
EM: kazuo@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, Yayoi, Tokyo, 113-0032 Japan
AU: Shinohara, M
T21C-0506 AF: ERI, Univ. Tokyo, Yayoi, Tokyo, 113-0032 Japan
AU: Yamada, T
T21C-0506 AF: ERI, Univ. Tokyo, Yayoi, Tokyo, 113-0032 Japan
AU: Uehira, K
T21C-0506 AF: SEVO, Kyushu Univ., Shimabara, Nagasaki, 855-0843 Japan
AU: Mochizuki, K
T21C-0506 AF: ERI, Univ. Tokyo, Yayoi, Tokyo, 113-0032 Japan
AU: Shiobara, H
T21C-0506 AF: ERI, Univ. Tokyo, Yayoi, Tokyo, 113-0032 Japan
AU: Sakai, S
T21C-0506 AF: ERI, Univ. Tokyo, Yayoi, Tokyo, 113-0032 Japan
AU: Kanazawa, T
T21C-0506 AF: ERI, Univ. Tokyo, Yayoi, Tokyo, 113-0032 Japan
AB: The Japan Sea is a typical back-arc basin in the northwestern Pacific. The Japan Sea seems to possess areas of various stage of back arc opening process. Information of a seismic structure is useful for consideration of the formation and development of the Japan Sea. Therefore many seismic surveys of crustal structures have been performed and several models for the formation of the Japan Sea have been proposed. However there is a little information of the seismic structure of the mantle beneath the Japan Sea. The deep seismic structure is essential for consideration of the opening of the Japan Sea because a mantle activity is thought to relate strongly to the opening. To obtain the deep structure of the eastern part of the Japan Sea, the long-term broad-band seismic observation had been carried out during three years in the Yamato Basin and Yamato Rise in the Japan Sea. From the long-term seismic observation, the seismic body waves passed through the mantle beneath the Japan Sea have been observed. The three-dimensional P- and S-wave velocity structures beneath the eastern part of Japan Sea are determined by travel time tomography method developed by Zhao et al(1992,1994). As a result, P and S wave tomographic images to a depth of 500 km beneath the Japan Islands arc and the Japan Sea are obtained. The region below the Japan arc island to a depth of 100 km has low velocity. This low-velocity zone continues to a depth of 300km beneath the Yamato Basin in parallel with the subducting pacific plate. In contrast, the region to a depth of 150 km beneath the Yamato Basin shows relatively high velocity. The obtained tomographic P-wave image has a high velocity anomaly in the mantle wedge extending down to a depth of approximately 150 km beneath the Yamato Basin. The regions where sea floor spreading is active at present usually have a low-velocity zone below a spreading center. From existence of the high velocity anomaly beneath the Yamato Basin, there is a possibility that the mantle activity did not play an important role in the formation of the Yamato Basin.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8100 TECTONOPHYSICS
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: Fall Meeting 2005