Study on Prospecting of Geothermal Reservoir by Seismic Noise Method.

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A Seismic noise survey was carried out in the Takinoue (Kakkonda) geothermal area, Iwate prefecture. 80 survey points are included in an area 6Km wide along the EW direction and 3Km long along the NS direction, centered in the Takinoue hot spring, and 40 survey points on measuring line between the Takinoue and Matsukawa geothermal areas. The relation between noise amplitude, distribution of dominant frequency and geothermal activity was investigated. The results are summarised as follows.1). Large amplitudes of seismic noise are observed in an area centered in the recent development zone and surrounded by Shironuma, the point half-way of the mountaineering path of Mitsuishiyama, the entrance to Kakkonda forest road, and south Shirasawa. The frequency of 5-15Hz is dominant in this area. On the otherhand, very small amplitudes of seismic noise are distributed to the south-east side of the Takinoue tunnel, the entrance to mountaineering path of Hiragakuranuma, and the downstream of Kakkonda river. The seismic noise in the frequency band 0.8-0.5Hz, which is dominant in this area, is considered to constitute the microseisms.2) Activities of fumaroles and hot springs are recognised at the area showing loarge amplitudes. It seems that the zone of generation of seismic noise is shallower than the geothermal reservoir.3). The seismic noise in the frequency band 2-15Hz is generated by the stream of steam and hot water going upwards form deeper reservoir to the surface.