On the results of geodetic observations of seismic effects

Abstract

1. 1. On the geodetic fundamental surveys in Japan (M. Tanaka) The Geographical Survey Institute has carried out fundamental surveys consisting of a precise geodetic survey, precise traverse, quadrilateral base line survey, leveling and astronomical observations. In several potential seismic areas which were specified by the Coordinating Committee for Earthquake Prediction mainly. The geodetic surveys have been speeded up to respond to the increased activity in earthquake prediction research. A short summary of the present state of geodetic surveys and some obtained results associated with earthquakes are reported. 2. 2. On the continuous observations of crustal movements (K. Hosoyama) More than forty crustal movement observatories of vault type, mainly belonging to universities, have been conducting observations with tiltmeters and strainmeters. Governmental institutions have intensified their routine monitoring of crustal movements in the Tokai and South Kanto districts, central Honshu. The observation network consists of 31 stations for ground strains by borehole strainmeters of the Japan Meteorological Agency (JMA), 15 borehole tiltmeter stations of the National Research Center for Disaster Prevention, and one monitoring chain of crustal activity observation stations of the Earthquake Research Institute of Tokyo University. About 20 tide gauge stations belonging to the GSI, JMA and the Hydrographic Office of Japan are also distributed in these districts. These crustal movement observatories have cooperated with each other for the purpose of studying the country-wide fields of coseismic strain and tilt steps in occasional major earthquakes. Qualitative agreement of observation with the seismic source mechanism was obtained in some cases.