Study on the Direction of Arrival of Geothermal Seismic Noise

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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.