地殻熱流量におよぼす熱水系の影響

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When we discuss the tectonics based on the terrestrial heat flow, we must consider the hydrothermal system which is a heat transfer mechanism in the earth's crust depending on the transport of water. This is more important in such areas having many hot springs as Japan (Figs. 1, 2). The hydrothermal system has a function of redistribution of the original terrestrial heat flow from the depths. If the hydrothermal system exists, therefore, it is possible that a high heat-flow region exists in the discharge area, and a low heat-flow region in the recharge area, even though there is no special heat source (Fig. 5). In this case, the excess of the conductive and conductive and convective heat discharge beyond the normal heat flow of the high heat-flow region must be equal to the shortage of the heat discharge below the normal value of the low heat-flow region. Meanwhile, if special heat sources are buried in the depth, the difference between the excess and the absolute value of shortage should come from the special heat sources. In Joban-Yumoto area, for example, any recent volcanic activity has not been known, there are large hot springs and their total heat discharge is about 4.1×10^7 cal/sec. If there was no special heat source in the depths, the extent of the hydrotherml system must be about 7, 000 km^2 wide. Otherwise, if the domain of the hydrothermal system is assumed to be a topographic basin (Fig. 4), the terrestrial heat flow under the hydrothermal system should have the value of 4.3 HFU. Another large extent of the hydrothermal system may exist in the south-westerm part of Hokkaido, where there are two adjacent areas of high-and low-heat flow, respectively (Fig. 6). Assuming the high heat flow area to be 2, 000km^2 wide, we can convert the conductive and convective heat discharges into the terrestrial heat flow of 6.3 HFU, which is composed of the mean value of the green tuff region, 2.6 HFU, the concentrated heat by the hydrothermal system, 2.2 HFU and the heat from the special heat sources, 1.5 HFU (Fig. 7). Generally, the values of heat flow redistributed by the hydrothermal system could be estimated if the areas of the system could be assumed. Then, we have laid a mesh with 20′×20′ lattices upon the map of Japan, and have assmed the area of this one square to be the area of the hydrothermal system for the hot springs within the square. And then, we calculated for 156 squares the quatients of the heat discharge divided by the area of the square. The quatients range from 0×10^<-1> HFU to 39×10^<-1> HFU, as shown in Fig. 8, and they are heat fluxes due to mass transportaion, that is, convective heat fluxes. Heat discharge from the ground surface can be expressed generally by the sum of heat fluxes due to conduction and convection. Therefore, in order to discuss the total heat flux, we have to add the values of convective heat flow to the ordinary terrestrial heat flow data. Finally, using such revised heat flow data, we can draw new contours of heat flow in Japan, as shown in Fig. 10. These contours are generally similar to that of ordinary conductive heat flow, but they may represent appreciably the anomalous thermal structures of Japan.
1973-12-01

地殻熱流量におよぼす熱水系の影響

スポンサーリンク

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スポンサーリンク