Study on the Direction of Arrival of Geothermal Seismic Noise

采用3分量1站法和三分量法分别对Kakkonda地热区和Hachimantai东部地区的地热地震传播进行了研究。使用NEC 9800计算机开发了软件来确定地震噪声传播的方向性。所得结果总结如下1。基于3分量1站方法的粒子运动和互相关研究发现，到达Kakkonda地热区的地热地震噪声的方向性与推测存在地热储层的方向不一定一致。然而，在确定地热地震噪声到达的方向时，考虑采用3分量1站观测，因为它可以通过在大量观测点进行调查来大致估计方向，并且即使在由于地形限制而不足以确保长测量线的地区，它也便于观测。在哈奇曼台东部地区的三方观测表明，该地区的地热地震噪声具有均匀的到达方向，并且起源于较深的地下区域。虽然由于对该地区地热构造的认识不足，还不能确定震源，但这表明该方法对地热储层的勘探具有一定的适用性。本研究建立了3分量1站和三方观测方法对到达地热区的地震方向性分析的基本体系。随着地热区数据的不断积累，需要进一步评价地热地震噪声测量的有效性。

Geothermal seismic propagation at the Kakkonda geothermal area and the eastern region of Hachimantai was investigated by the 3 components - 1 station method and tripartite method respectively. Softwares were developed using an NEC 9800 computer to determine the directionality of seismic noise propagation. The results obtained are summarized as under.1. The directionality of geothermal seismic noise arrival at the Kakkonda geothermal area investigated by the particle motion and cross correlation based on the 3 components - 1 station method does not necessarily coincide with the direction of a geothermal reservoir presumed to exist. However, 3 components - 1 station observation is considered for determining the direction of geothermal seismic noise arrival, since it enables approximate estimation of the direction by undertaking survey at a large number of observation sites and it facilitates observation even at areas not large enough to secure long measuring lines due to topographic limitations.2. Observation by the tripartite method at the eastern region of Hachimantai showed that the geothermal seismic noise at this region had a uniform direction of arrival and was originated from a relatively deep subterranean area. This suggested the applicability of this method to the prospecting of a geothermal reservoir, although the source of tremor cannot be affirmatively specified due to inadequacy of knowledge on the geothermal structure of this area.3. In this study, a basic system could be established for the analysis of the directionality of tremor arrival at geothermal areas by the 3 components - 1 station and tripartite observation methods. Further evaluation of the effectiveness of geothermal seismic noise survey is required by accumulation of survey data at an increased number of geothermal areas.