木戸（仲佐）/ゆかり

講演予稿:
　海洋科学技術センターのかいれい／よこすか調査船にて，１９９７年度 より３成分地磁気測定を行っており，そのデータがかなり まとまってきたので，報告する．特に，日本海溝と南海トラフ沿いで 測定されており，両者の磁気異常の比較から，潜り込みにともなう プレートの特性の一部を明らかにすることができた．

abstract:
　The R/V Kairei and R/V Yokosuka have conducted several complementary geophysical surveys of the Japan Trench and Nankai trough in 1997 and 1998. The purposes of this study are threefold (1) to identify and quantify on a fine scale crustal velocity and magnetic susceptibility variations; (2) to interpret the area's deformation history, and; (3) to elucidate the dynamic mechanisms by which deformation occurs in circum-Japanese subduction zones. Shipboard three-component magnetic (STCM) data were acquired during legs KR97-04, 05, 06, 07, 09, KR98-04, 06, 07, and YK98-02 leg 2, and analyzed to reveal geomagnetic features landward and oceanward of the trench axis. The vessels surveyed approximately 20 NE-SW-, 10 N-S-, and 10 E-W-oriented lines off the coast of Fukushima during the 100 days of surveying. Furthermore, at least two figure-eight maneuvers were performed during each leg to estimate shipboard magnetization effects. 8 Hz data were filtered to remove noise and sampling bias, and analyzed to determine whether anomalous features were essentially two- or three-dimensional. The resulting dataset has been combined with simultaneously acquired swath bathymetry and gravity data to facilitate interpretation. The data reveal pervasive magnetic lineations aligned NE-SW and NW-SE on the oceanward and landward sides respectively of the Japan Trench. In comparison, magnetic lineations on either side of the Nankai Trough are aligned N-S. We infer the different lineation orientations in relation to the two trench axes to reflect different thermal structures in the slabs. Future work within the framework given above is planned to ascertain the significance of these features and their orientations with respect to the Japan Trench and Nankai Trough.

キーワード:
地磁気異常，日本海溝，南海トラフ，プレート，潜り込み

Keywords:
Manetic anomaly, Japan Trench, Nankai Trough, Subduction