Abstract
Data of geophysical observation during the period from July 1984 to December 1986 are analyzed. The data include measurement results of groundwater temperature, ground strain and water level in wells in the Tokai district, the central part of Japan. The main purpose of our observation is to catch a precursory phenomenon which is expected to appear before the occurrence of the ‘predicted’ Tokai earthquake. Ordinary behaviors of the variation of the monitoring data are investigated in special connection with the effects of some environmental elements such as atmospheric temperature, atmospheric pressure and rainfall. No definite relation has yet been found between earthquakes and the observed quantities. However, a large spike-shaped change, observed in the water temperature at the Oshima site prior to the eruption of Mt. Mihara in November 1986, suggests a possibility that other spike-shaped changes, hitherto regarded as noise, may be significant.
