| Title | Geophysical Monitoring in the Sengan (Hachimantai) Thermal Area, Northeaset Japan |
|---|---|
| Authors | Toshiyuki Tosha and Mituhiko Sugihara |
| Year | 1997 |
| Conference | Japan International Geothermal Symposium |
| Keywords | |
| Abstract | Microearthquakes monitoring has been carried out in the Kakkonda geothermal field, which is one of the most active geothermal field in Sengan thermal area. Comparing seismicity in the geothermal field, number of earthquakes, especially those in the reinjection field, has decreased. The decrease of events and change of distribution of earthquake suggests the change ofcharacteristics of reservoir in the Kakkonda geothermal field. Another geophysical monitoring is the precision gravity survey in the Sumikawa geothermal field, where a new geothermal power plant began operation in 1995. The increase in gravity was detected in the reinjection field, which was predicted by computer reservoir simulation. Geological Survey of Japan (GSJ) has been carrying out geophysical monitorings at two geothermal fields in the Sengan thermal area. One is microearthquake monitoring in Kakkonda and the other is gravity monitoring in Sumikawa. In both geothermal field repeated self-potential surveys have been also performed for several years. Some of studies in the Sengan thermal area are reviewed in this paper. Sengan thermal area is located between Morioka and Akita prefectures and is one of the most well known thermal area. There are four geothermal power plants, Kakkonda, Matsukawa, Sumikawa and Onuma, and many hot springs in it. Late Tertiary and Quaternary volcanism is dominant in the thermal area overlying Miocene and pre-Tertiary sedimentary rocks. Geological and geophysical features on the Sengan area are studied under one of Japan's sunshine projects, which focused on geological and geophysical surveys over wide thermal area in Sengan and the other area. |