抄録
The γ-ray survey using a multichannel analyzer (hereafter called MCA) with NaI (Tl) scintillation counter was carried out across the Obaku active fault, which is extending to about N-S direction in southern part of Kyoto Prefecture. This study reveals the increase of γ-radiation due to 214Bi and 40K over the fault plane necessarily coincides to each other. The increase of γ-radiation due to 214Bi is clearly attributed to the radioactive decay of gaseous 222Rn emanating through the active fault plane, while the increase of γ-radiation due to 40K attributed to the concentration of potassium in the artificial works and biogenic products may be superimposed on the increase by the dissolution of potassium from rocks and adsorption to clay minerals along the active fault plane. It is considered that the accurate location of active fault can be recognized by the peak intensity of γ-ray radiating from 214Bi.
The γ-ray measurement by MCA shows that the Obaku fault is assumed as an active fault, which is composed of, at least, three parallel fault planes in the fracture zone of about 100m width extending to N10°W direction.
