HR: 1340h
AN: OS23A-1038    [Abstracts]
TI: A seismic reflectivity study of the methane hydrate layer in the offshore area, southwestern Taiwan
AU: * Cheng, W
EM: wbin@just.edu.tw
AF: Jinwen University of Science and Technology, 99 Ann Chung Road, Hsin-Tein City, Taipei County, 236, Taiwan
AU: Yang, H
EM: grace571u@yahoo.com.tw
AF: Jinwen University of Science and Technology, 99 Ann Chung Road, Hsin-Tein City, Taipei County, 236, Taiwan
AU: Lee, C
EM: leecs@mail.ntou.edu.tw
AF: Institute of Applied Earth Science, National Taiwan Ocean University, Keelung, Taipei County, 200, Taiwan
AU: Wang, T
EM: tkwang@mail.ntou.edu.tw
AF: Institute of Applied Earth Science, National Taiwan Ocean University, Keelung, Taipei County, 200, Taiwan
AU: Liu, C
EM: csliu@ntu.edu.tw
AF: Institute of Oceanography, National Taiwan University, Taipei, Taipei City, 104, Taiwan
AU: Wang, Y
EM: wangys@linx.moeacgs.gov.tw
AF: Central Geological Survey, Ministry of Economic Affairs, Taipei, Taip[ei, 236, Taiwan
AU: Chen, S
EM: songlin@moeacgs.gov.t
AF: Central Geological Survey, Ministry of Economic Affairs, Taipei, Taip[ei, 236, Taiwan
AB: In this study we present the result of an investigation of the regional variation behavior in bottom-simulating reflector (BSR) reflectivity of the gas hydrate-bearing sediments in the offshore, southwestern Taiwan. We focus on the analysis and interpretation of airgun-array signals recorded by ocean bottom seismographs (OBSs) during 2004 and 2006. Eight profiles of seismic reflection/refraction with a total length of about 140 km and recorded by 50 recovered OBSs were acquired on the active and passive margins in offshore southwestern Taiwan. The profiles of the 2004 and 2006 profiles are oriented in E-W and N-S direction and the 2005 survey is trending in NW-SE perpendicular to the continental margin. For all the OBS lines, amplitudes of the direct water arrival, the multiple, and the BSR were picked interactively. A quantitative representation of reflector strength is provided by calculation of reflection coefficients. In general, the seafloor reflection coefficients for the active and passive margins are estimated as 0.1-0.25. Maximum of up to 0.47 were observed over the topographic high in the active margin. Those high amplitudes of seafloor reflection could be associated with widespread carbonate pavement observed with TowCam in the active and passive margins, southwest Taiwan. For the BSR the largest reflection coefficients were observed in the passive margin. This area has average values of about 0.12 with localized highs between 0.15 and 0.18, while the active margin area exhibited relatively lower values of about 0.015-0.05. If we assumed that the velocity below the BSR has a constant value. Variations in BSR reflection coefficients are attributed to velocity variations of the gas hydrate above the BSR. Estimates of the hydrate concentration have been made from BSR reflection coefficients obtained in this study. Mean concentration are abut 20~25% of the total sediment volume for the passive margin, and are about 5~10% for the active margin. The results of calculated reflection coefficient of the BSR in offshore SW Taiwan suggest that inferred hydrate concentration for the passive margin profiles is relatively higher than that for the active margin profiles.
DE: 0702 Permafrost (0475)
DE: 0704 Seasonally frozen ground
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3004 Gas and hydrate systems
DE: 3036 Ocean drilling
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting