HR: 11:35h
AN: T12B-06    [Abstracts]
TI: Seepage at western Sagami Bay, Central Japan: Results from heat flow and seismic reflection
AU: * Kinoshita, M
EM: masa@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima, Yokosuka, 237-0061 Japan
AU: Machiyama, H
EM: bucci@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima, Yokosuka, 237-0061 Japan
AU: Yamashita, M
EM: mikiya@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima, Yokosuka, 237-0061 Japan
AU: Soh, W
EM: soh@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima, Yokosuka, 237-0061 Japan
AB: The Izu Peninsula on the Philippine Sea Plate (PHS) collides NNW-ward with the mainland Honshu. The subduction boundary at the northern boundary of PHS is thus distorted northward, forming an oblique subduction boundary Sagami Trough to the east of Izu Peninsula. Also a fault plane is inferred at the western Sagami Bay off Hatsushima Island, in order to explain tremors activity. The volcanic front of IBM arc runs at the western Sagami Bay, producing a group of monogenetic volcanoes. Active cold seep communities develop off Hatsushima at 1200 m water depth. Intensive heat flow studies, including dive results and recent survey in 2004 revealed a high heat flow distribution (> 1,000 mWm-2) within 500m of the colony and low (~50 mWm-2) on the Sagami Trough to the east. Hydrological conduit along the potential fault or along the lithologic boundary will feed nutrients to the colony, as well as it will provide heat conductively in the surrounding region. Dive studies revealed almost zero heat flow within 50 m of the colony, whereas heat flow is as high as 20,000 mWm-2 on the colony. Continuous monitoring of heat flow in and outside the colony (only 1m apart) was conducted for 4 years using JAMSTEC_fs cabled observatory. A temperature decrease by 0.8°C only at sensors 10-20 cm below seafloor within the colony occurred within two months. Piston core samples taken in 2003 include massive carbonate crust of 20 cm thickness, which probably forms a hydrological seal. This suggests that the hydrological system here is dynamically supported through time-variant chemical reaction and fluid transport. In 2005 we conducted a grid survey of single-channel seismics at 0.1-0.2 miles interval around the Hatsushima seep community. A potential reservoir, showing negative reflectivity, was located 200-300m below sea floor. We plan to submit a drilling proposal to IODP in this area, in order to characterize hydrological system trough sampling and long-term monitoring.
DE: 3015 Heat flow (benthic)
DE: 3021 Marine hydrogeology
DE: 3025 Marine seismics (0935, 7294)
DE: 3036 Ocean drilling
DE: 3050 Ocean observatories and experiments
SC: Tectonophysics [T]
MN: Fall Meeting 2005