Study on Prospecting of Geothermal Reservoir by Seismic Noise Method.

在岩手县的Takinoue （Kakkonda）地热区进行了地震噪声调查。以竹上温泉为中心，在东西向宽6Km、南北向长3Km的区域内，共设80个测点，在竹上与松川地热区之间的测量线上设40个测点。研究了噪声幅值、主频率分布与地热活动的关系。结果总结如下。在最近的开发区内，被四沼、三井山登山路线的中途点、Kakkonda森林道路的入口和白泽南部包围的区域观察到大振幅的地震噪声。5-15Hz的频率在这个区域占主导地位。另一方面，在竹上隧道东南侧、平谷沼登山通道入口和Kakkonda河下游分布着非常小的地震噪声。考虑以0.8 ~ 0.5 hz频带为主的地震噪声构成微震。2)在振幅较大的区域可以识别出喷气孔和温泉的活动。地震噪声的产生区似乎比地热储层浅。2-15Hz频段的地震噪声是由深层储层的蒸汽和热水向上流到地表产生的。

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.