Abstract
A very accurate system to observe the temperature change of a deep ground-water has been developed. A specially made quartz crystal is adopted as a sensing unit which enables the temperature measurement to the accuracy of 1/1, 000°C. Other advantages of the system are the simplicity of the instrument, ease of the installation, and low cost, which make possible a number of installations in an area. The concentration of the observations is especially important since the natures of wells might be different from place to place.
More than 25 sets of the instruments were made and 15 sets have been already installed in Hokkaido and Honshu.
According to the preliminary results, a coseismic signal was observed at a well in eastern Hokkaido when an earthquake of magnitude 7.5 took place at the distance of 200km. Other than the coseismic signal, a number of unexpected temperature variations have been observed.
