Terrestrial heat flow in Japan

Terrestrial heat flow has been determined at 58 localities (39 on land and 19 in the sea) in and around the Japanese Islands. The average values of observed heat flow on land and in the sea are 1.55 × 10−6 and 1.30 × 10−6 cal/cm2 sec, respectively. The out-standing features of the heat-flow distributions are as follows: (a) Regions of high heat flow (Q > 2.0 × 10−6 cal/cm2 sec) exist in the Japan Sea side of the Honshu arc. (b) The region of high heat flow seems to extend, through the Fossa Magna area, down to the Izu-Marianne arc. (c) It is probable that a similar zone of high heat flow exists in the inner side of the Kurile arc. (d) These zones of high heat flow precisely coincide with the zones of the late Cenozoic tectogenesis in the area, (e) Low heat flow (Q < 1.0 × 10−6 cal/cm2 sec) prevails in the Pacific coast side of northeastern Japan and in the oceanic areas directly east of it. (f) The region outside these zones of high and low heat flow has heat flow that is within the range of normal values. Various hypothetical processes, such as the distribution of radio-activity in the crust, upheaval and denudation of the land, subterranean chemical reactions, thermal refraction, and mantle convection, have been examined in order to account for the observed heat-flow distribution. Owing to the uncertainty of assumed quantities, it is difficult to determine which hypothesis should be selected.