抄録
There are many fumaroles and hot springs in the Takenoyu geothermal area. Heat discharge and 1m depth temperature survey were carried out for identifying the thermal structure of this area. The high temperature ground extends along the Takenoyu fault which is assumed geologically. The total heat discharge by conduction, hot springs, and fumaroles was estimated to be 1.5×106 cal/sec. The underground temperature distribution to depths up to 1000 m was obtained from logging data of 14 wells. The temperature beneath the shallow hot area is higher than the beneath its surroundings. The maximum temperature exceeds 200°C at a depth of 600 m. As no cap rock is assumed beneath the Takenoyu geothermal area, we tried to explain the surface heat discharge and the underground temperature pattern by the two-dimensional thermal convection model for the opened geothermal reservoir. As a result, the following model was suggested; the meteoric water infiltrating into the underground encounters the heat source of 250°C and 900m wide which is stretching horizontally at a depth of 600 m. After heated there, it rises up to the surface and makes thermal manifestations within a width of 600m. The heat discharge and underground temperature distribution calculated from such a model agree well with the observed ones.