Abstract
The first order triangulation in Japan had been carried out twice for 1882-1911 and 1948-1967. Change in angle for the above period at every station is illustrated in Fig. 2. Changes of all sides are illustrated in Fig. 3. Such areas as changes in angles are more than 3".0 correspond to the areas deformed violently by the destructive earthquakes that exceed 7.0 in magnitude. Change in angle is about 1".0 at half of the stations. The standard deviation of an observed angle is 0".7. Accordingly, there is perhaps very 19ttle deformation of the crust in these areas. The figure of deformation vectors found in the case that the triangulation is adjusted whole Japan as a single net is already reported in Fig. 8 in [1]. The very remote vectors from the datum station in the figure are influenced uniformly by accumulated errors. Consequently, we cannot know intuitively minute relative deformation of the crust in these areas. In order to avoid the above inconvenience we choose five stations whose numbers are written in Fig. 2 from the quiet zones of crust movement, and give forcibly their positions old results and adjust again whole Japan as a single net. The vectors obtained by the above method are shown in Fig. 4, five fixed stations are indicated with circles in the figure. The figure expresses clearly the movement of the crust caused by destructive earthquakes. Fig. 4 shows also the fact that there are many blocks of various sizes in horizontal movement of the crust.
