Abstract
The 1st order triangulation near the Suruga Bay, Honshu, Japan was carried out three times in 1883/1891, 1931, 1973 respectively. The earth's horizontal strains were deduced from these survey data. In the first report [1], net adjustment of the triangulation in 1931 was carried out under the assumption that the positions of the two stations, KENASHIYAMA and DAIMUGENYAMA, are not changed during 1883/1891-1931 . In the second report, geodetic positions of the three stations, TANZAWAYAMA, KENASHIYAMA, and DAIMUGENYAMA in 1931 are deduced from the survey data that are obtained under the assumption of some fixed stations located far from the discussed region. These estimated positions of the three stations are adopted in the net adjustment. Net adjustments of the triangulations in 1883/1891 and 1973 are the same as in the first report. Directions of two principal strain axes and maximum shear strain in each geodetic triangle in the second report are the same as in the first report, while dilatation and side-length changes are different each other. Horizontal displacement vectors of the triangulation stations during 1883/1891-1931 are obtained referring to the fixed stations far from the convergent boundary of the Philippine Sea plate. From these data, it is concluded that the Izu peninsula is drifting to NNW by 2.3 cm/yr and the Tokai district is compressed to NNW by 1.1 cm/yr.
