Heat flow measurements in the northern part of Honshu, northeast Japan, using shallow holes

Abstract

Abstract One of the most notable features of heat flow distribution in the Japanese Islands is the existence of a low heat flow zone on the Pacific Ocean side of the Northeast Japan Island Arc and a high heat flow zone on the Japan Sea side. However, the detail of the transition between the low and high heat flow zones has not been apparent because of the lack of available deep holes. Heat flow measurements in the transition zone have been made using shallow holes. By the combined use of a new multisensor long-term underground temperature recording system and conventional techniques, four reliable heat flow values were obtained in the transition zone. The results show that the heat flow value increases steeply from the aseismic front (20–40 mW/m2) to the volcanic front (120–130 mW/m2). If the heat transfer in the crust is conductive, the temperatures beneath the aseismic front and the volcanic front at the depth of 30 km will be about 100°C and about 1000 °C, respectively.