日本における過去60年間の上下変動

II.関東地方南部

抄録

In succession to the preceding paper in which the secular variation in the physical height of the datum was clarified, heights of the bench marks along the leveling loop in the southern part of the Kanto District are calculated in this paper. This loop is adjacent to the Tokyo loop, and 5 epochs of leveling, i. e., 1884. 7, 1896.4, 1925. 3, 1931. 2, and 1950.7, are selected. Moreover, the leveling loop in Izu Peninsula (epochs: 1904. 1, 1926. 9, and 1931.0), the leveling route along the western coast of Miura Peninsula (epochs: 1898. 9, 1925. 2, 1930.4, add 1952. 8), and the route between Hachioji and Totsuka (epochs 1926.0, 1930.4, and 1952.8) are added. These leveling loop and routes are shown in Fig. 1. Collecting all these heights of bench marks, the crustal movements during the respective epochs are calculated, and the results are shown as the contour maps of equal movement in Figs. 3, 4, 5, and 6. In the duration concerned, the Great Kanto Earthquake (Sep. 1, 1923) and the Izu Earthquakes (March, May and November in 1930) are involved. Accordingly, it can be considered that Fig. 3 shows the pre-seismic movements before a group of such great earthquakes, Fig. 4 shows mostly the abrupt movements due to the Great Kanto Earthquake, Fig. 5 shows the resultant of the movements due to the Izu Earthquakes and the recovery movements of the preceding earthquake, and Fig. 6 shows the post-seismic movements. For the sake of comparison, the movements of Figs. 3 and 6 are reduced to the annual movements in Figs. 7 and 8. It is clearly seen that the general tendencies of pre- and postseismic movements are reversed on the whole.