Distribution Characteristics and Nationwide Assessment of Geothermal Resources in Japan

Abstract

The tectonic setting in which the Japanese Islands located is an arc-trench system. Almost all Japanese high-temperature geothermal systems have their heat sources of the late Quaternary magma chambers, and high-temperature geothermal systems are distributed along the volcanic fronts of eastern and western Japanese arcs. As can be seen typically in the Tohoku (northeast Japan) area, the volcanic front area lies in steep mountainous topography that is an adverse condition for resource development.

Distribution of high-temperature geothermal systems becomes more sporadic toward the back-arc side. Some medium-temperature geothermal systems are distributed along the Japan Sea side, and they may be able to be utilized for small-scale binary-cycle power generation. Geological Survey of Japan (GSJ) and National Institute of Advanced Industrial Science and Technology (AIST) have conducted nationwide geothermal resource assessment by the volume method twice. They used different estimation method of subsurface temperature distribution and calculation of the basement rock depth. The calculated values are ca. 20,500MWe and ca. 23,500MWe. Considering the accuracy of the estimation of underground temperature distribution, they are considered to nearly identical result calculation results.

As for the relation to the natural parks, more than 80 percent of the high-temperature hydrothermal resources was calculated to be distributed in the special protection zone and special zones (class I to III) of natural parks. Among these protected zones, geothermal resources concentrated in the special protection zone and the class I special zone. But the special protection zone and the class I special zone often cover the central part of volcanoes such as craters, and there might be some difficulty in developing such areas. The distribution of geothermal resource is independent of artificial range setting of natural parks, and survey data in national parks are critically insufficient. Implementation of exploration in national parks is desirable to clarify the situation of the endowment of geothermal resources in these areas.