Tadashi Kanagawa

4. In situ stress measurements in the Japanese islands: Over-coring results from a multi-element gauge used at 23 sites

Abstract The authors have developed a new over-coring stress relief method with a multi-element strain gauge. The new gauge has been used to estimate in situ stress at more than 20 sites for electric power stations in Japan. The results of in situ stress measurements obtained by the method exhibit a general tendency that the maximum compressive principal stress acts horizontally and the horizontal to vertical stress ratio exceeds 1.0. The directions of maximum horizontal compressive in situ stress obtained by the method seem to be consistent with those of the geodetic strains calculated from first order triangulation survey data, and with those estimated from the distribution of tectonic zones which have become active in the Quaternary period. The Japanese islands are located in a tectonically active region, i.e. they are situated near the eastern boundary of the Asian plate towards which both the Philippine Sea plate and the Pacific plate advance. For further detailed discussion a more refined analysis would be required; however, the in situ stress in the Japanese islands is likely to have been significantly affected by these crustal movements.