Revisiting the Anomalously High Natural Heat Discharge in the Izu Peninsula, Japan

Abstract

There have been many interesting studies so far, geochemical and geophysical, on the nature of thermal discharge from the earth’s deeper part, specifically referring to the Izu Peninsula, central part of Japan. The peninsula was formed by the collision of the Philippine Sea Plate to the thicker crust of the southwestern end of northeast Japan, therefore it is situated at a tectonically singular position. For example, Okubo et al. (1983) have compiled the data of underground temperatures measured in deep wells distributed over the whole area of Izu Peninsula, and they classified the area into three different types of geothermal regime: up-flow dominated, down-flow dominated, and thermal conduction dominated regimes. One remarkable fact is that the thermal conduction dominated area in the southernmost part of the peninsula, which contains the township of Minami-Izu, is characterized by very high heat flow value at about 120 - 150 mW/m2 even though we can find no very young volcanic activity there. In view of other geoscience data obtained up to present time, a review is made of the observed heat discharge in the area, and some discussions are given on the possible mechanisms to explain its anomalous characteristics.