HR: 1340h
AN: V13B-1352    [Abstracts]
TI: Mini 3D seismic surveys of mud volcanoes in the Kumano Basin
AU: * Nakamura, Y
EM: saru@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1, Minamidai, Nakano, Tokyo, 1648639, Japan
AU: Morita, S
EM: morita-s@aist.go.jp
AF: National Institute of Advanced Industrial Science and Technology, Site C-7, 1-1-1 Higashi, Tsukuba, 3058567, Japan
AU: Ashi, J
EM: ashi@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1, Minamidai, Nakano, Tokyo, 1648639, Japan
AB: Kumano Basin is a forearc basin of the Nankai Trough subduction zone. Eight mud volcanoes have been found in the basin from previous diving and side-scan sonar surveys. Seismic sections clearly showed the BSR widely developed in the basin. The existence of the BSR near the mud volcanoes suggest that the methane gas dissociated from the hydrate excesses the activity of the mud volcanoes. To reveal the relation between activity of mud volcanoes and hydrate, we have conducted mini 3D seismic experiments. The experiments were separated to two phases; first experiment was conducted in 2004 covering Daigo and Dairoku Kumano Knolls (KK5 and KK6), and second was in 2006 covering Daisan Kumano Knoll (KK3). KK5 is located close to KK6 so they are called as twin mud volcanoes. Previous observation by diving and result from piston core sample analysis revealed following features;
•KK5 is active now, or has been recently active.
•KK6 is not active now. It stopped the activity at ~25,000 years ago.
•KK3 is not active now, but it had been active more recent than KK6.
We investigated the structure in and around the mud volcanoes in different phases of activity. All of three mud volcanoes studied have 'umbrella structure' beneath the seafloor. This structure is onlapped by the surrounding sedimentary sequence, which suggests that the 'umbrella structure' was formed by the ancient mud volcanism buried by the basin sediment. In KK3, accumulation of the umbrella (three or four times) is observed. This indicates the KK3 has been activated periodically in the last 500,000 years. BSR is continuously traceable beneath KK6, but it is vanished beneath the center of KK5. Beneath KK3, the BSR is also vanished just beneath its center, but the area without BSR is narrower then KK5. The observation on the BSR would suggest strong relationship between mud volcano activity and gas-hydrate.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3004 Gas and hydrate systems
DE: 3025 Marine seismics (0935, 7294)
DE: 8426 Mud volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting