The γ-ray intensity around and about active faults are discussed from the two view points. One is the relation between γ-ray intensity distribution and active faults. The other is a variation of γ-ray intensity before and after earthquakes. The γ-ray intensity is proportional to Radon emanation which is always emanated from the Earth's surface to the atomosphere. Radon emanation is known to be large on and around the active faults. So that, survey of γ-ray intensity must be useful to search and detect active faults.
On and around several active faults, γ-ray surveys are carried out and the segments of active faults are found to be associated with large intensity of γ-ray. A few of them can be deliniated with the direction of the strikes. Some earthquakes are occurred during the surveys. Logical consideration conjectures a decrease of γ-ray intensity after an earthquake. Really, after the events a decrease of γ-ray intensity is observed for all the earthquakes. And at the time of the vibration by the blasts, γ-ray intensity shows clear decrease.
Continuous observation of γ-ray at Yamasaki Fault Observational Station supports the above observational results. These investigations give a method of studies on active faults and indicate possibility of earthquake prediction.