Thermal Gradients of Deep Wells and their Terrestrial Heat Flows in Central and Southwest Japan

Abstract

Deep wells, having about 1, 000 m depth, were drilled at Takarazuka City, Ichinomiya-Cho, and Yabu-Cho, Hyogo-Prefecture, Omachi City, Nagano Prefecture and around Tango Peninsula, Kyoto Prefecture. Terrestrial heat flow determined at Takarazuka and Yabu is less than 2.0 HFU (84 mW/m²), that around Tango Peninsula and Ichinomiya more than 2.0 HFU, and that at Omachi more than 2.7 HFU (113 mW/m²). From these results, it is concluded as follows: (i) the heat flow of the northern part of Kinki District is higher than that of the southern part. This has already been pointed out by Uyeda and Horai (1964), and (ii) the heat flow determined at the western part of Omachi City, of which rock body is Ariake granitic body, is more than 2.7 HFU. Nishimura and Mogi (1986) showed that the thermal origin of the Kurobe hot dry rocks was the residual heat of the granitic body and the seismic wave was attenuated in this region (Fukao and Yamaoka, 1983). These facts indicate that the temperature of this granitic body is high and has residual heat in the central part of this body.