Geophysical Exploration of the Northern Hachimantai Geoghermal Field

Abstract

The northern Hachimantai geothermal field is located in the backbone ranges at the northern parts of Akita and Iwate Prefectures. It has been explored and developed by Mitsubishi Metal. Corporation since 1965, and a 10 MW power plant is now under the testdriving.
The geophysical results obtained through the exploration may be summarized as follows:
1) The regional gravitational survey indicates that the geothermal field occupies a part of the regionally depressed zone along the western flank of the backbone ranges.
2) A remarkable negative anomaly is found in the depressed zone. This is considered an ancient caldera or crater.
3) The electrical survey reveals many occurrences of hydrothermal reservoir. A sheared zone confirmed by the seismic method is interpreted as the conduit for the geothermal water.