HR: 0800h
AN: T41A-1162    [Abstracts]
TI: Seismic and Acoustic Evidence of a Large Seafloor Gas Seep on the Miyako Section of the Okinawa Trough
AU: * Luan, X
EM: xluan@nrcan.gc.ca
AF: Instittue of Oceanography, Chinese Academy of Sciences, 7 Nanhai Rd, Qingdao, 266071 China
AB: A marine geophysical survey was carried out, by the R/V Science 1 of the Institute of Oceanography, Chinese Academy of Sciences (IOCAS), in the year 2000, on the Miyako Section of the Okinawa Trough. Here we present seismic and acoustic evidence of a gas seep on the seafloor on the western part of the Okinawa Trough, near the lower slope of the East China Sea Slope, and discuss the possibility of related formation of gas hydrate. A gas column reflection was observed in echo-sounder data above a section where the seafloor reflector was missing, in both the echo-sounder and the seismic data for line H14. The seismic data also show an acoustic curtain reflection and a turbidity reflection at this section. These anomalies are evidence of the existence of a gas seep, which occupies an area 2.2km in diameter. Based on the acoustic curtain on line H14, we believe that the amount of gas contained in the sediments below the gas seep is larger than 1% by volume of sediment. Tectonically, the gas seep developed in a small basin controlled by basement uplift in the north, south and in the east. The thickness of the sediment layer can be greater than 3.5km. A mud diapir structure was found in layer D beneath the gas seep. Over-pressure may occur due to the large sediment thickness and also the tectonic basement uplift in the north, south, and east. The mud diapir could be the preferential pathway for methane-rich fluids. The acoustic curtain may indicate that free gas related to the gas seep can be formed on the seafloor. Judged from the temperature and the pressure, and the estimated heat flow data, a gas hydrate layer exists above the acoustic curtain seems reasonable.
DE: 1744 Tectonophysics
DE: 0910 Data processing
DE: 0930 Oceanic structures
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting