Horizontal Crustal Movement in KANTO-TOKAI District (IV) (V)

Abstract

This is the fourth and fifth reports in the series discussing horizontal crustal move ments in the Kanto and Tokai district, Japan. Some triangulation stations were destroyed or moved during the repeated works and these are checked. The damaged are 9% for the period from 1882/1902 to 1924/1926, 8% for the period from 1882/1902 to 1931, 23% for the period from 1882/1902 to 1973/1980 and 21% for the period from 1924/1926 to 1973/1980. The displacement vectors for the damaged stations are not calculated. The results of calculation for displacement vectors are summarized as follows: 1) The detected displacements are closely associated with the 1923 Kanto earthquake for the period from 1882/1902 to 1924/1926. In the south Kanto district, magnitude of the displacements are as large as 2?`4 meters, and orientation of the vectors is toward the sea, while the displacement vectors in the north part of the Izu peninsula are very small in their magnitudes. 2) In the north part of the Izu peninsula, the displacement vectors for the period from 1882/1902 to 1931 are associated with the 1930 Kita-Izu earthquake, which seems to be the after shock of the 1923 Kanto earthquake. In the south part of the Izu peninsula, orientation of the displacement vectors is toward NNW and magnitude of the vectors are almost 1 meter. The crustal strain in this area was unreleased during the discussed period. 3) The displacement vectors for the periods from 1924/1926 to 1973/1980 and from 1931 to 1973/1980 are not affected by any large earthquake. The displacement vectors are quite reversed in the south Kanto district as compared with the coseismic one. 4) The displacement vectors for the period from 1882/1902 to 1973/1980 are affected by the 1923 Kanto and the 1930 Kita-Izu earthquakes in the Kanto district, while in the Tokai district the displacement vectors show the stationary and accumulated crustal movement which is not affected by large earthquakes. 5) The stationary crustal movement in the Kanto-Tokai district is estimated as a few cm/yr in the rate and NNW in the direction. The horizontal crustal move ment quite depends on the NNW drifting of the Philippine Sea plate.