| Title | 3D Magnetotelluric Survey at the Yanaizu-Nishiyama Geothermal Field, Northern Japan |
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| Authors | Toshihiro Uchida, Shinichi Takakura, Takumi Ueda, Masaho Adachi, Hitoshi Ozeki, Kunikazu Kamada, Tatsuya Sato |
| Year | 2011 |
| Conference | Asian Geothermal Symposium |
| Keywords | magnetotelluric survey, 3D inversion, geothermal reservoir, Yanaizu-Nishiyama |
| Abstract | We conducted three-dimensional (3D) magnetotelluric (MT) survey at the Yanaizu-Nishiyama geothermal field, Fukushima Prefecture, northern Japan, where a 65 MWe geothermal power plant has been in operation since 1995. The purpose of the survey was to obtain a detailed electrical resistivity image around the geothermal reservoir over the field, where a sophisticated electromagnetic survey was not conducted since the exploration stage of the geothermal field in 1980s. The 3D MT measurement was carried out at 30 locations in 2010. In addition to these, we utilized existing MT data obtained for a 2D MT survey by the Geological Survey of Japan in 2000 and 2001. Sixteen stations from this existing MT dataset were used for the 3D interpretation. The resistivity model obtained by a 3D inversion indicates clear upper and lower boundaries of the clay cap layer over the geothermal reservoir. Distribution of feed zones recognized in production boreholes is confined below the lower boundary of the low-resistivity clay cap. The shape of the low-resistivity layer also shows a good correlation with the distribution of underground temperature. |