ボアホール計器による地殻変動連続観測

―埋込式体積歪計による観測―

抄録

Japan Meteorological Agency (J. M. A.) is now operating borehole volume strainmeter at thirty one stations in Tokai and Kanto districts. Its main purpose is to catch the precursory phenomena of a great earthquake which is said to possibly occur in Tokai district. However the output signals of the instruments are mixed with various noises from different kinds of sources. To accomplish the main purpose, it is necessary to know the instrumental responses to these disturbances which may contaminate the useful informations. In this paper the instrumental responses of the borehole volume strainmeter to the seismic wave incidence, atmospheric pressure changes and earth tides are reviewed, which has been revealed up to the present. The results are summed up as follows. The observation sites which have high sensitivities to the seismic waves give large amplitudes of earth tides, but do not respond well to the atmospheric pressure change. One of the main causes which give the varieties of these sensitivities is considered to be the difference of Poisson's ratio in each site. Step-like volumetric strain changes due to influences of groundwater and precipitation are also discussed briefly.