Abstract
A three-dimensional seismic survey off Shimokita Peninsula, NE Japan revealed a number of typical deformations due to slumping and the related dewatering in the Pliocene and younger sedimentary sequences. The slumping was generated primarily by layer-parallel slip on a very gentle continental slope. The slump units often exhibit an imbrication structure formed by repeated thrusting in the bottom layers. The dewatering structure is observed as widespread parallel dikes of which distribution is strongly dependent on the imbrication of the slump units. By tracing seismic layers, slip planes of the slumps proved to be generally characterized as low-amplitude layers having some thickness, and some of the slip planes exhibit flattened features under the slump units of the imbrication structure accompanied by parallel dikes. This implies that excess fluid in the slip plane was drained through the parallel dikes during slumping and that the excess fluid in the slip plane caused the lubrication to enhance the slumping. In the survey area, high methane flux has been reported, and natural gas-related structures, e.g., gas chimneys, have also been observed. These features are considered to be typical of such a high-methane-flux continental slope, and the high methane flux should be an important ground instability factor to cause the slumping and the dewatering phenomena.
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Acknowledgments
The authors would like to express their appreciation to JOGMEC for permitting use of the seismic data, METI fundamental seismic survey 2008, Sanriku-oki 3D. We would also like to thank the reviewers, Drs. Yuzuru Yamamoto and Toshiya Kanamatsu, and the editor, Dr. Kiichiro Kawamura, who were involved in this paper.
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Morita, S., Nakajima, T., Hanamura, Y. (2012). Possible Ground Instability Factor Implied by Slumping and Dewatering Structures in High-Methane-Flux Continental Slope. In: Yamada, Y., et al. Submarine Mass Movements and Their Consequences. Advances in Natural and Technological Hazards Research, vol 31. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-2162-3_28
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DOI: https://doi.org/10.1007/978-94-007-2162-3_28
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