| Title | Geological Structure and Subsurface Temperature Distribution in the Wasabizawa Area, Akita Prefecture, Japan |
|---|---|
| Authors | Tsuneshi Inoue, Masaru Suzuki, Keiichi Yamada, Masaru Fujita, Shinzi Huzikawa, Shigehisa Fujiwara, Ichiro Matsumoto and Koji Kitao |
| Year | 2000 |
| Conference | World Geothermal Congress |
| Keywords | geology, temperature, Wasabizawa field |
| Abstract | The subsurface data obtained from more than 60 wells mainly drilled by New Energy Development and Industrial Technology Development Organization (NEDO) and Dowa Mining Co., Ltd. since 1974 indicates that the geology of the Oyasu-Doroyu hot spring area have four major structural features. The Kijiyama-and Kawarage-basins are characterized by very thick Miocene acidic pyroclastics and the Oyasudake-and Okumaemori-uplifts have very shallow Pre-Tertiary metamorphic and granitic basement rocks intruded by Tertiary intrusives. A very extensive exploration program (recently undertaken in the Wasabizawa area by NEDO under the new survey program ìCî of the ìGeothermal Development Promotion Surveyî) revealed that the area, which had been considered simply as part of the southeastern extension of the Okumaemori uplift, is separated into a horstand- graben structure defined by NE- and NW-trending faults. Maps showing subsurface temperature contours at 100-m intervals ranging from +400 to ñ800 m (elevation) have been presented based on data including static temperature profiles obtained from new wells drilled during the recent exploration project. All maps show a similar pattern, with high temperature in the Uenotai and Wasabizawa areas, separated by a low-temperature trough extending along the Doroyu fault. In the Wasabizawa area, it is suggested that, at 500 m below sea level, all areas are within temperature contours of 220oC or higher, and all maps show the contours are open to the SE, toward Yamabushidake and Takamatsudake mountains, indicating that the source of geothermal fluid and the heat source lie in that direction. Two separate high-temperature trends distinguished in the maps at elevations from +400 to ñ 200 m (elevation) suggest that the flow pattern of geothermal fluid is strongly controlled by the NW-trending fault system. |