Report on DELP 1989 Cruise in the TTT Junction Areas : Part 1: General Outline | 1989年度DELP海溝三重会合点海域調査研究航海報告 : 第1部:概要

この報告では主として1989年度DELP計画によるDELP-89研究航海の成果を記述する.この航海目的は1984年度頃より得られた詳細な海底地形及び地磁気・重力探査等の調査結果の成果などから得られた,地震構造,海上地磁気異常,海底地殻熱流量の測定値分布などの結果を総合して,この地域のプレート衝突境界の状況をより明確にしようとするものである.この部分(Part 1)では1989年度DELP研究航海計画の目的,航海海域及び測線・測点,航海期間,観測項目,データ整理方法等について記述する.最後に今日までに得られた成果を参照してテクトニクス的議論を行う.なお地震探査,地磁気探査,地殻熱流量探査の各項目についてはそれぞれPart 2-4で詳述される.

This report describes mainly the results of a DELP research cruise in 1989 to the western part of Sagami Trough off southern coast of Kanto Plain, and the trench-trench-trench triple junction off the Boso Peninsula, Kanto, Japan. The cruise was planned as one of the programs of a joint study by two DELP seafaring research groups, JGDGBAB and JDRGDSOL (refer to authorship footnotes). Preliminary results of studies on the seismic structures, heat flow , and marine geomagnetic measurements are obtained with the aim of clarifying the geometrical and mechanical scheme of the collision and subduction between two oceanic plates, the Philippine Sea Plate subducting underneath the North American Plate (Japan land mass), and collision and distortion among three plates: Pacific Plate, Philippine Sea Plate and North American Plate (Japan land mass). The concept 'Japan land mass'does not seem to be equivalent to the plates, but we use this term because it is not unequivocally understood whether the northeastern-eastern part of the Japan land mass, including the Kanto Plain, Tohoku and Hokkaido, belongs to the North American Plate or the Eurasian Plate (eg. Seno, 1985). However, we prefer to assign this part of the Japan land mass to the North American Plate all through this article just for convenience in spite of its ambiguity. The scientific objectives, area surveyed, cruise period, terms of observation, filing of data, and names of participants in this program, and some of the main results and interpretations obtained so far, are presented in Part 1. More details of data acquisition, analysis and interpretation are presented in the later parts. Also described in Part 1 are some new results and findings obtained very recently at the time of this writing and not mentioned in other parts. Data and interpretation obtained by other cruises related to the present program are also referred to in the concluding section of this part.