日本における過去60年間の垂直変動

I.総論および原点の永年変化

抄録

The precise leveling in Japan commenced in 1884, and 80 years have passed away since then. During this period, the greater part of the leveling lines was revised at least twice, and even several times on some lines. But they were too fragmentary both in region and in revision years. Therefore, in order to obtain the vertical movements of the crust in the whole land of Japan, a certain systematic course of reduction is necessary. The outline of the course of reduction adopted is:(1) To derive the secular variation of the physical height of the Tokyo datum.(2) Using this variation, to derive the secular variation of the height of each bench mark which constitutes the Tokyo loop surrounding the datum (in these bench marks, the junction marks to the adjacent loop are involved).(3) To choose a certain epoch with a range of±3 years so as to unify the revision years on the adjacent loop.(4) To read the heig of the junction bench mark corresponding to this epoch, and to make it a given condition in the reduction of the adjacent loop.(5) To extend this procedure to the next loop or net one after another. In this paper, after the general discussion on the reduction of the precise leveling, the secular variation of the physical height of the Tokyo datum is derived by using the similar variations of several bench marks which surround the datum and locate on the stable pleistocene layer of the Musashino Plateau. The numerical value is given by the relation (A).