しんかいで地磁気を測る Near-bottom Magnetic Measurements with Submersible Shinkai 6500

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Author(s)

    • 富士原 敏也 Fujiwara Toshiya
    • 独立行政法人海洋研究開発機構・地球内部変動研究センター Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology

Abstract

海底に近い場所で地磁気を測ると, 高分解能地磁気異常が得られ, 海洋地殻の詳細な磁化構造や, 海洋地殻に記された古地磁気変動を調べることに役立つ. 潜水調査船を利用した地磁気調査では, 磁力計のシステムが簡便である, 海底の画像や採取試料等の他の観測情報が同時に入手できる等の長所がある. 潜水船は海底直上を移動できるので, 数mの分解能が期待できる. 「しんかい6500」に深海磁力計を搭載しての地磁気観測が幾度か行われてきた. それらにより観測経験の蓄積,研究成果が積み重ねられてきた. 一方で, 計測に関しての問題点も次第に浮き彫りにされてきている. 潜水船は地質観察優先の高度, 航行をすること, センサーの設置位置, 短い測線長などの制約により, 地磁気測定に適したオペレーションを実現し難い. 地磁気データのキャリブレーション法, オペレーション法には改善の余地が十分にあり, 今後の検討が肝要である. 潜水調査船で海底に近づいて観測することならではの長所を生かした地磁気観測は, 潜水船観測の幅を拡げ, 海洋底調査研究に非常に大きな効力を発揮することができると期待される.

Near-bottom magnetic measurements provide us high-resolution magnetic anomaly. The high-resolution anomaly is valuable for the studies of the detailed magnetization structure of ocean crust and paleointensity recorded on the ocean crust. The measurements using a submersible have advantages to make the magnetometer system simple and to incorporate other observational results obtained by the submersible, such as seafloor pictures and samples that are informative for geology. A submersible usually moves at a height of several meters above seafloor, therefore the magnetic anomaly has a resolution of several meters. Magnetic measurements using the submersible Shinkai 6500 have been conducted several times, and experiences and scientific results have been accumulated. On the other hand, problems regarding the magnetic measurements were brought out. Because the submersible observation usually gives priority to geological observation, the navigation is not suitable for magnetic measurements. The restricted sensor position and the short track length are also disadvantages for the magnetic study. There is room for improvement in the magnetic calibration and operation. For the future, improvement of the measurement method is critically important. The near-bottom magnetic measurements with the submersible expand the range of the submersible study and provide additional information about lithology which may not be visible at the seafloor, and the seafloor age with a high resolution.

Journal

  • JAMSTEC Report of Research and Development

    JAMSTEC Report of Research and Development (2009), 111-122, 2009

    Japan Agency for Marine-Earth Science and Technology

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