Subsurface temperature in non-Quaternary volcanic regions in Japan

Yamakawa, Tadashi; Takeda, Seiji ; Kimura, Hideo; Hyodo, Hiroshi*

Radionuclide migration toward human society through geologic processes is to be assessed as part of safety assessments of geologic disposal for radioactive waste. A subsurface temperature in non-Quaternary volcanic regions was focused as one of the changes in this study. The study was conducted to extract features of subsurface temperature in non-Quaternary volcanic regions throughout Japan. After delineating Quaternary volcanic regions, features in non-Quaternary volcanic regions were studied in various aspects. The present study clarified that a relationship between subsurface temperature and its depth was expressed by an equation in non-Quaternary volcanic regions far from about 24 km of Quaternary volcanic centers. This led to about 16C/km in general geothermal gradient in non-Quaternary volcanic areas, which was lower than 20C/km of the previous study.