Geothermal Exploration in the Sengan Area, Akita and Iwate Prefectures, Northeast Japan

Abstract

The Sengan area islocated in Akita and Iwate Prefectures in the northern part of Northeast Japan. In this area, there are active volcanoes, hot springs, fumaroles and three geothermal power plants at Matukawa, Onuma and Kakkonda. Geothermal explorations have been carried out with various kind of surface surveys and many structural borings in this area. At first, the wide-ranged and deep geothermal reservoir was expected to be in Neogene formations, and hopeful heat source was also expected to be the magma chamber related to the Tamagawa Welded Tuff (Early Quaternary Pyroclastics). However, the 1,5OOm class structural borings proved that the heat potential of this area is low than the expected heat potential. Therefore, the studi.ed area was spread to the north part where Quaternary andesite are distributed. These explorations revealed that young volcanoes (Mt.Akita- Yake- Yama and Mt. Hachimantai volcanoes) are expected to be the h e at source of this geothermal system.