TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 50 (Nos. 11, 12), pp. 905-911, 1998

Development of instruments for seafloor geodesy

Hiromi Fujimoto1, Kin-ichiro Koizumi1, Yukihito Osada1, and Toshihiko Kanazawa2

1Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan
2Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan

(Received April 2, 1998; Revised July 3, 1998; Accepted July 17, 1998)

Abstract: We have developed systems for measuring differential displacements across a fault zone, and examined their resolutions through seafloor experiments at relatively short baselines. A system for a seafloor extensometer makes use of precise acoustic ranging with a linear pulse compression technique. The system has a resolution better than 1 cm in acoustic ranging over a baseline of at least 1 km. The most critical problem is correction for temperature variations, and we estimate that the effect can be corrected with cm-order accuracy in the case of a deep-sea experiment. We have also examined a leveling system on the seafloor using an array of ocean bottom pressure gauges and an ocean bottom gravimeter to detect differential vertical motion. The system is estimated to have a resolution of several centimeters in vertical displacement. These system will be useful for triangulation and leveling on the seafloor, but we need further studies over a longer baseline and to achieve better long-term stability.

Corresponding author E-mail: fujimoto@ori.u-tokyo.ac.jp

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