Horizontal Crustal Movements in the Kanto-Tokai District, Japan, as Deduced from Geodetic Data

Abstract

Fujii, Y., and Nakane, K., 1982. Horizontal crustal movements in the Kanto-Tokai district, Japan, as deduced from geodetic data. In: P. Vyskočil, A.M. Wassef and R. Green (Editors), Recent Crustal Movements, 1982. Tectonophysics , 97: 115–140. The Kanto and Tokai district, Japan, is located very close to the northern convergent boundary of the Philippine Sea plate and has been attacked by great earthquakes several times during the historic past. This district has been resurveyed several times since the first observation. The authors compiled all the geodetic data and deduced the horizontal crustal movements. In the new net-adjustment for geodetic network, the six stations, Tsukubasan, Teruishizan, Dodairayama, Kokushidake, Kaikomagadake, and Enasan are assumed not to have moved during the observational period. The horizontal displacement vectors for four periods are deduced. Also error ellipses of displacement vectors are estimated. The earth's crustal strains are calculated from obtained vectors. It is concluded that the Kanto district is compressed from ocean to inland during the interseismic period and reversed completely by faulting during the 1923 Kanto earthquake. The secular rate of north-northwest displacement of the triangulation stations close to the Sagami trough is estimated to be of the order of ˜ 3 cm/year. The Tokai district has been compressed from ocean to inland during the past 90 years except for the western part where the 1944 Tonankai earthquake occurred. The tectonic strain field in the Kanto-Tokai district is expressed by a line of contraction. The observed compression and extension cycle is due to north-northwest drifting of the Philippine Sea plate and reverse faulting along its convergent plate boundary. The results of geodetic observations and unified net adjustments considering their possible errors completely revealed the earthquake cycle.