本州中央部の地殻の水平変動と被害地震との関係

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The first order triangulation was carried out twice in 1883-1889 and 1952-1963 in Central Japan. In order to elucidate the relation between the horizontal deformation of the earth's crust and destructive earthquakes, the author analyzed the data by the following method. The triangulation stations on the ellipsoidal surface are projected on the plain. Supposed the deformation in a triangle composed of three stations expressed as a linear function of x and y components, the displacement of the station, dilatation, rotation, maximum shear and axes of principal strain are calculated for each triangle as shown in figures 3 to 8. The results are as follows. I. The triangulation stations are displaced northwestwards radically in Tohoku district. On the other hand, they are rotated counter clockwise in Hokuriku, Kanto and Tokai districts (Fig.-3). 2. The dilatation domain is distributed from Tohoku to the inland of Kanto and Chubu districts. The contraction domain is distributed along the coast of Hokuriku. Along the coastal region of Kanto and Tokai, dilatation domains are arranged alternately at 50-60 km intervals (Fig.-4). 3. The crust is rotated counterclockwise in Tohoku-Hokuriku, central Kanto, and the belt area from Mikawa Bay toward the district of the NE direction. On the other hand, it is rotated clockwise along the Pacific coast of Tohoku, southern Kanto-Tokai district, central Niigata Prefecture and the area from Hida mountainous district toward the SW direction (Fig.-5). 4. In most area of Tohoku district, both strain axes are dilated. In Hokuriku district, contraction strain axis is arranged concentrically, and the contractive strain axes are larger than dilated strain axes. In the northern and eastern parts of Kanto district, the dilatation strain axis is run in N-S direction. It is radiated in the western part of the district. In Tokai and Chubu districts, the dilatation strain axis is run uniformly in NW-SE direction (Fig. 6-7). 5. Maximum shear zone of 10^<-5> order is distributed in the area from Tohoku district through the SW part or Niigata Prefecture to Tokai along Itoigawa-Shizuoka tectnic line, and it is done in the area from northern part of Boso to Ise Bay along the coast (Fig.-8). 6. The destructive earthquakes have occurred in the area, where the maximum shear is 10^<-5> and over(Fig.-8).
1981-03-30

本州中央部の地殻の水平変動と被害地震との関係

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