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Intensity of γ-ray has been observed for the purpose of investigating its relationship to earth-quake occurrence since June, 1981. Five regions each of which contains several observation pointshave been set up along two active faults, Shikano and Yoshioka, which ruptured at the time of theTottori earthquake, 1943 (M=7.4). The observation has been done at each point once a month, while some test observations of γ-ray were made at and near the Tottori Microearthquake Obser-vatory, in order to examine daily variation of γ-ray intensity and its correlations to meteorologicalelements and others.The intensity of γ-ray is the largest in Hosomi region which is in hilly area and along the Shikanofault. Observations just on these two faults seem to show somewhat higher intensities than thoseof other points, or to show large dispursion. Intensities measured on Aug. 3, 1981 were the largestin the whole observation period at all points, although the reason is not clear yet.Seismic activity, especially along the Shikano and Yoshioka faults, was examined in somedetail in the period of the present observation, but more investigations are needed in order to discussabout the relations between γ-ray intensity and seismic activity.

The observation of γ-ray intensity has been done on and near the Shikano and Yoshiokafaults once a month since June, 1981. On the other hand, fundamental observations havebeen carried on at a standard point near the Tottori Microearthquake Observatory.Continuous observation of γ-ray intensity was carried out for successive 2 days at thestandard point, and an interesting phenomenon was observed. Namely, the γ-ray intensityincreased suddenly, continuing for about 5 minutes in the rain, and restored to the normalvalue again.Pattern of temporal change of γ-ray intensity is considered nearly the same amongseveral observation regions in a period of one and a half years since June, 1981.A decreasing of intensity was observed at nearly the same time in July, 1982 in manyobservation regions. More detailed investigation is necessary, however, in order to determinewhether this decreasing is significant or not, and, if so, whether it is related to the earth-quake occurrence or not.

Continuous observation of r-ray intensity has been made at the observation vault attachedto the Tottori Microearthquake Observatory for the purpose of investigating the relationbetween earthquake occurrence and r-ray intensity.From the results for about 40 months it is elucidated that r-ray intensity shows an annualvariation and has approximately negative and positive correlations to atmospheric pressureand temperature, respectively.It was ascertained that the r-ray intensity commences to show abnormally large valuesa few months before the occurrence of nearby earthquakes with relatively large magnitude, say, greater than 4.5.

Yumura fault is located in northwestern part of Hyogo Prefecture, Southwest Japan. Ithas ENE-WSW direction and more than ten km-length from Kasumi-Cho to Onsen-Cho. Andit is said that the Yumura fault was related to generation of the Yumura hot spring.The survey of r-ray intensity was carried out on and near the Yumura fault in order tolocate the fault, and 737 observation points were utilized.The contour map of r-ray intensity in the area concerned was made by YHP 9845b. Highintensity areas of r-ray are located in the central zones and low intensity areas in the northernand southern parts. It was estimated that the Yumura fault is located in a transition zone fromlow to high intensity areas.R-ray intensities were measured on 8 routes at an interval of 20 m. In this analysis, ther-ray intensity at each point was plotted as a function of S-N coordinates of observation points, and this graph shows the existence of several parts of high and low r-ray intensities. It is in-ferred that transition points from high to low intensities agree with the fault line.In the Yumura spa area, the highest part of r-ray intensity accorded well with the partin which hot springs concentrate and therefore the temperature is high.