| 講演要旨(和文) | | 海上反射法地震探査で観測されるWrap-around多重反射波は、その繰り返し性のため海中の諸現象について検出する能力を秘めているが、これまで有効利用されてきた例は存在しない。2次元反射法地震探査で観測されたデータを丹念に調べることにより、Wrap-around多重反射波が強い擾乱を受けている海域を特定した。その海域には、メタンハイドレートあるいはメタンガスの存在を示唆するBSR (Bottom Simulating Reflector)イベントやガスの流通経路の役割を果たす断層の存在が確認された。従って、Wrap-around多重反射波の強い擾乱は海中に漏洩するメタンガスの可能性があることを示唆する。予察的な数値シミュレーションを行ったところ、この示唆を支持する結果が得られた。 |
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| | 講演要旨(英文) | | Seismic wrap-around multiples which are produced by the previous shot and trapped between sea surface and flat seabed in the two-dimensional (2D) marine seismic reflection data, have a potential to provide information about oceanographic phenomena because their repetition in the water column could influence seismic wave propagation. By focusing on the disturbance of wrap-around multiples, we imply the possible presence of methane gas bubbles emitting from seafloor over several kilo-meters within a submarine canyon with a flat seabed. We observe the significant disturbance of wrap-around multiples in both pre-stacked gathers and common mid-point (CMP) stacked sections, which may be caused by methane bubbles. The existence of a bottom simulating reflector (BSR) implies the existence of methane gas, and the existence of a fault beneath the specific event, which could be a pathway of methane gas flows to the seafloor, provides an indirect evidence of gas bubble seeps. Furthermore, we conduct preliminary numerical simulations of acoustic wave propagation to investigate the cause of disturbances of wrap-around multiples. Our preliminary numerical simulations imply that the disturbance of wrap-around multiples might be associated with the internal scattering caused by an aggregation of gas bubble seeps in the water column. |
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