Natural Gamma-Ray Spectrometry for Yata Active Fault Area in Kinki District, Southwest Japan
Yousuke Noumi
Department of Geosphere-Biosphere System Science, Faculty of Informatics, Okayama University of Science, Japan
Keiichi Nishimura
Department of Geosphere-Biosphere System Science, Faculty of Informatics, Okayama University of Science, Japan
Jyunpei Akamatsu
Disaster Prevention Research Institute Kyoto University, Gokano-sho, Uji 611-0011, Japan
要旨
Yata fault is one of the active faults in Kinki district, south-west Japan. The fault activity is medium class and also its activeness in the past time is not clear. For estimating the fault condition near the ground surface, the natural gamma-ray survey using a multichannel gamma-ray analyzer with NaI scintillation detector was carried out over the Yata fault area. Natural gamma-ray spectral data were corrected at 44 sites by field survey. The fluctuation of natural radioactive nuclides 40K, 214Bi and 208Tl were mined from the gamma-ray spectral data, and the fluctuation ratio of 214Bi/40K, 214Bi/208Tl was mapped on the study area using GIS software. The result shows the fluctuation ratios of southeast area were higher than another area, where the geologic boundary has discontinuity on the fault line. The difference of these patterns of fluctuation ratio 214Bi/40K and 214Bi/208Tl were due to weathering situation of the host rocks. The southeast block of Yata fault area may have been moved recently.
