The Geological Survey of Japan started to carry out the basic geothermal survery at the beginning of 1973 FY. In that survey, the selected thirty geothermal areas shown in the figure 1 are being surveyed by geological, geophysical, and geochemical methods to develop geothermal exploitation at each area. This is the first systematic project conducted by the Government for geothermal exploration in Japan. In each area, hydrothermally altered zones are mapped and the measurement of natural heat

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... charge including shallow temperature survey is done. Geophysical prospecting (electric and gravimetric methods) and geological mapping are applied at some of them. Collecting chemical data of hot spring is also done at the most of places. The results of these exploration work are utilized to decide the sites for the proceeding drilling. At each area, a few wells of about five hundred meters depth are drilled by the government to know the underground geothermal structure. This drilling