Gas seepage on the sea floor of Okinawa Trough Miyako Section  

作　　者：LUANXiwu QINYunshan 

机构地区：[1]InstituteofOceanography,ChineseAcademyofSciences,Qingdao266071,China

出　　处：《Chinese Science Bulletin》2005年第13期1358-1365,共8页

基　　金：surpported by the Chinese Minister of Science and Technology(Grant No.G2000046703).

摘　　要：A marine geophysical survey was carried out, on the R/V Science 1 of the Institute of Oceanography, Chi-nese Academy of Sciences (IOCAS), in 2000, at the Miyako Section of Okinawa Trough. Here we present seismic and acoustic evidence of a gas seep on the sea floor on the western part of the Okinawa Trough, near the lower slope of the East China Sea Slope and discuss the possibility of related forma-tion of gas hydrate. A gas column reflection was observed in echo-sounder data above a section where the sea floor reflec-tor was missing, on 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 the evidence of the existence of a gas seep, which occupies an area 2.2 km 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 east. The thickness of the sediment layer can be greater than 3.5 km. 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 tec-tonic 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 sea floor. We also note that the layer above the acoustic curtain on profile H14 may contain gas hydrate.A marine geophysical survey was carried out, on the R/V Science 1 of theInstitute of Oceanography, Chinese Academy of Sciences (IOCAS), in 2000, at the Miyako Section ofOkinawa Trough. Here we present seismic and acoustic evidence of a gas seep on the sea floor on thewestern part of the Okinawa Trough, near the lower slope of the East China Sea Slope and discuss thepossibility of related formation of gas hydrate. A gas column reflection was observed inecho-sounder data above a section where the sea floor reflector was missing, on both theecho-sounder and the seismic data for line H14. The seismic data also show an acoustic curtainreflection and a turbidity reflection at this section. These anomalies are the evidence of theexistence of a gas seep, which occupies an area 2.2 km in diameter. Based on the acoustic curtain online H14, we believe that the amount of gas contained in the sediments below the gas seep is largerthan 1 percent by volume of sediment. Tectonically, the gas seep developed in a small basincontrolled by basement uplift in the north, south and east. The thickness of the sediment layer canbe greater than 3.5 km. 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 inthe north, south, and east. The mud diapir could be the preferential pathway for methane-richfluids. The acoustic curtain may indicate that free gas related to the gas seep can be formed on thesea floor. We also note that the layer above the acoustic curtain on profile H14 may contain gashydrate.

关 键 词：气体流量 冲绳岛 地震 海底运动 预测方法 

分 类 号：P315[天文地球—地震学]