HR: 1340h
AN: T13B-0457    [Abstracts]
TI: Detailed Seismic Image of Mud Volcones in Kumano Basin
AU: * Nakamura, Y
EM: saru@ori.u-tokyo.ac.jp
AF: ORI, Univ. Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AU: Ashi, J
EM: ashi@ori.u-tokyo.ac.jp
AF: ORI, Univ. Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AU: Morita, S
EM: morita-s@aist.go.jp
AF: AIST Geolog Surv Japan, Site 7 1-1-1 Higashi , Tsukuba, 305-8567 Japan
AU: Mochizuki, K
EM: kimi@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Kumano basin is one of the forearc basins located landward of the Nankai trough. Seven mud volcanoes have been observed and investigated in and around the Kumano basin using side scan sonar imagery, core sampling and dive observations, however, the deep structure of these mud volcanoes have not been precisely investigated. To elucidate the deeper structure beneath the mud volcanoes in the Kumano basin, we conducted a mini 3D seismic survey at Daigo and Dairoku Kumano knolls in June 2004. A 600m-long, 24 channel streamer cable and a GI gun with 150 in ³ chamber were used in this survey. The GI gun was fired in the True GI mode to generate high frequency source signal. R/V Tansei-maru kept her speed at ~3kt against the ground and fired the GI gun every 10s. The seismic data were stacked with water velocity onboard for the quality control purpose. The 5 days survey concluded into 34 basic seismic lines of 5km long, with 100m interval to cover the Daigo and Dairoku Kumano knolls, and 16 additional 2.5km-long seismic lines which cover the Daigo Kumano knoll at 50m interval together with the basic seismic lines. Result of 2D post stack migration shows detailed sub-sea image in and around the mud volcanoes. The mud volcanoes were surrounded by the Kumano basin sediments with ~0.5 s of TWT. Anticline shaped reflectors were observed beneath the mud volcanoes. Small scale anticlinal structure was found beneath the both sides of the slope of Dairoku Kumano knoll. The structure imaged within the mud volcanoes should be deeply related with the history of their activity. The BSR is well developed at 0.5 s in TWT beneath the seafloor around these mud volcanoes but the BSR is terminated beneath the center of Daigo Kumano knoll. On the other hand, the BSR exists beneath the Dairoku Kumano knoll. The previous piston coring and side scan sonar surveys suggested that Dairoku Kumano knoll has not been active for long time but Daigo Kumano knoll has been active. The difference in the existence of the BSR is strongly related with the difference in the activity of these mud volcanoes. Further study including 3D seismic data processing will be conducted in the future.
DE: 3004 Gas and hydrate systems
DE: 3025 Marine seismics (0935, 7294)
DE: 8003 Diapir and diapirism
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005