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Foldback reflectors near methane hydrate bottom‐simulating reflectors: Indicators of gas distribution from 3 D seismic images in the eastern N ankai T rough
Author(s) -
Otsuka Hironori,
Morita Sumito,
Tanahashi Manabu,
Ashi Juichiro
Publication year - 2015
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/iar.12099
Subject(s) - geology , facies , trough (economics) , clathrate hydrate , reflection (computer programming) , petrology , perpendicular , seismology , methane gas , amplitude , methane , geomorphology , hydrate , geometry , optics , ecology , chemistry , physics , mathematics , organic chemistry , structural basin , biology , computer science , economics , macroeconomics , programming language
Understanding of fluid behavior and gas distribution in the shallow subsurface are important considerations in gas hydrate formation and the global carbon cycle. Estimation of gas distribution based on reflection seismic surveys, however, is difficult because the boundary of a gas‐bearing zone is indistinct and not systematically defined. This study reports distinctive features related to gas‐hydrate distribution and possible fluid migration in high‐resolution 3 D seismic‐reflection data from sediments of the eastern N ankai T rough. These features, here termed foldback reflectors ( FBRs ), descend in accordion shaped reflectors near the edges of bottom‐simulating reflectors ( BSRs ). FBRs generally correspond to lateral boundaries between two seismic facies, a ‘dimmed’ facies with relatively low amplitude and subdued high‐frequency components beneath the BSR and the contrasting facies around the BSR . The dimmed facies corresponds to areas of anomalously low velocity consistent with a small amount of free gas. FBR is mostly developed in well‐stratified formations in uplifted regions. Dip directions of the FBR appear to be restricted by orientation of the host formations. Edges of the FBR often correspond to high‐amplitude layers. Such occurrences of FBR suggest that regional uplift and layer‐parallel fluid migration are related to the formation of FBR as well as BSR .