Technical Note 20/6

LEG 186


Modified by K. Suyehiro from Proposal 431 Submitted by:

K. Suyehiro, H. Fujimoto, T. Kanazawa, J. Kasahara, Y. Fukao, H. Momma, K. Fujioka, T. Matsumoto, J. Kinoshita, S. Sacks, A. Linde, R. Hino, A. Hasegawa, M. Shinohara, and I. Kawasaki

Staff Scientist: Gary Acton --- Co-Chief Scientists: Kiyoshi Suyehiro and Selwyn Sacks


During Leg 186, we will drill two sites from the deep-sea terrace on the landward side of the Japan Trench off northeast Japan to monitor crustal response to stable (aseismic) or unstable (seismic) sliding of the subducting Pacific Plate. This will be the first attempt to establish such a long-term seafloor borehole observatory in one of the world's most active and most studied subduction zones. Near-field data from an active plate boundary are crucial in quantifying the plate's elastic and anelastic behaviors in relation to earthquakes. Borehole strainmeters and broadband seismometers will be installed at the bottom of the two holes to continuously monitor strain changes and seismic activities associated with episodic plate motions. Secondary objectives include (1) determining the forearc subsidence history and placing constraints on the subduction mass balance at this tectonic erosional environment and (2) obtaining arc volcanism reference since 3 Ma.

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