5. Studies of the Thermal State of the Earth. The 13th Paper: Terrestrial Heat Flow in Japan. : A Summary of the Terrestrial Heat Flow Measurement in Japan up to December, 1962

Since 1957, terrestrial heat flow has been determined at 39 places on the Japanese Islands by the Earthquake Research Institute, University of Tokyo. Besides these, 12 sea measurements have been made in the sea around Japan as a joint program of the University of Tokyo and the Japan Meteorological Agency.Of the total of 39 land stations, 26 are metal mines, 4 coal mines, 2 oil fields, 3 natural gas fields, 1 railway tunnel and 3 sites of other types. In each of these stations heat flux was estimated from the geothermal gradient combined with the thermal conductivity of rocks in which the thermal gradient was measured. An outline of the method used to measure thermal gradients and thermal conductivity is described. Temperatures were measured in deep or in short bore holes for geothermal gradient assessment. The maximum depth of temperature measurement exceeded several hundred meters at most of the land stations. In the course of the temperature measurement, two types of underground isothermal surfaces were discerned and their origin investigated. Values of the thermal gradient on land varied from 0.5° to 5.0℃/100m; except those areas which are considered to be geothermally anomalous. Thermal conductivity was determined by the divided-bar method. The apparatus was calibrated with standard substances of knownconductivity. In the course of this study, measurements were made on over 240 sets of rock samples covering 36 rock types. In this paper, the results are presented in a diagram according to theirrock types. These values range from 2×10-3 to 15×10-3 cal/cm sec ℃. Errors accompanying the calculation of heat flow values wereestimated from the probable variation in the thermal gradient andthe degree of ambiguity in assessing the in situ thermal conductivity of the strata as based on the thermal conductivities ofindividual samples. In most cases, the error amounts to a fewtenths of 1 μcal/cm2 sec or 20 to 30 per centum of the observedheat flow value. From the 39 land and 12 sea measurements, general tendencyof terrestrial heat flow distribution in and around Japan can bevisualized. Characteristic features of the distribution are as follows: i) A region of high heat flow exists on the inner side of the Japanese arc, where the heat flow value exceeds 2 μcal/cm2 sec. ii) A region of low heat flow (less than 1 μcal/cm2 sec) exists on the Pacific Ocean side of north-eastern Honshu, iii) There may be a high heat flow region in the Pacific far off the coast of north eastern Honshu, iv) In regions other than the above, almost all the heat flow values on land are between 1 and 2 μcal/cm2 sec.東京大学地震研究所によつて1957年以来行なわれてきた地殼熱流量の測定は1962年12月までに,日本各地の39地点で行なわれた.他に気象庁と協同して行なつた海洋観測によつて,海域にも12地点での測定結果がある.陸上で行なった39の測定のうち,26は金属鉱山,4は炭砿,2は油井,3は天然ガス井,1は鉄道遂道,他の3はその他の目的のために掘塹された試錐孔を利用したものである．地殼熱流量は地下温度増加率と地層の熱伝高率の積として求めた

Studies of the Thermal State of the Earth. The 12th Paper : Terrestrial Heat Flow Measurements in Hokkaido District, Japan

Terrestrial heat flow was measured at 6 localities in Hokkaido District. Of these 6 localities, 3 (Akabira, Ashibetsu, Haboro) are coal mines and the other 3 (Shimokawa, Konomai, Toyoha) are metal mines. Geothermal gradient was assessed from underground temperature distribution measured in each of these localities. The gradients are 2.48℃/100 m at Akabira, 3.08℃/100 m at Ashibetsu, 4.54℃/100 m at Haboro, 2.84-3.24℃/100 m at Shimokawa and 3.81- 4.10℃/100 m at Konomai. In Toyoha, the gradient amounts to 11 ℃/100 m. Geothermal heat flux was calculated combining the thermal gradient with thermal conductivity of rocks in each locality. The values of flux are 1.07 × 1O-6 cal/cm2 sec in Akabira, 1.35 × 1O-6 cal/cm2 sec in Ashibetsu, 1.87 × 10-6 cal/cm2 sec in Haboro, 1.60-1.82 × 10-6 cal/cm2 sec in Shimokawa, 2.44-2.63 × 1O-6 cal/cm2 sec in Konomai, and in Toyoha the flux seems to exceed 5 × 10-6 cal/cm2 sec. The results seem to indicate that the heat flow exceeds 2 × 10-6 cal/cm2 sec in the western and northeastern parts of the District, while other areas show moderate heat flow i.e. on the 1 × 10-6 cal/cm2 sec level.1.北海道地方の6地点で地殼熱流量測定を行ない,この地方の地殼熱流量分布について基本的な傾向を知ることができた.個々の測定点に関する要点を以下に述べる