On the γ-ray measurement around the Yamasaki fault

A γ-ray survey was carried out around the Yamasaki fault. The results were not so clearly interpreted as were made around the Ohbaku fault. An earthquake of magnitude about 4 occurred near the fault on Sept. 30, 1977. On 27 points among the survey lines above mentioned, time variation of γ-ray intensity was examined by 4 times of measurements, one of which was before the earthquake and the rest after it. The pattern of the variation is similar to that of Chloride ion contents (Yoshioka (7)) in a spring near the fault. This suggests us that the continuous observation might have caught some precursory change of the earthquake occurrence. From the middle of Nov. continuous observation was started in the observation tunnel of crustal movements at Yasutomi. It seems that high values of γ-ray intensity arise about 4 days after the peaks of the numbers of the microearthquakes and explosions near the region. (author)