Study on Characteristics of Geothermal Seismic Noise by Array Observation

采用三分量法和频波数法分别对kakkonda地热区和Hachimantai东部地区的地热地震传播进行了研究。研究了1 ~ 10Hz范围内地震噪声的到达方向和视相速度。结论可总结如下1。kakkonda地热区地震噪声到达方向无日变化和长期变化。在热采井关闭井口阀前后，改变了汽供系统附近的到达象限。3 ~ 7hz的地震噪声来自地热储层方向。在1 ~ 10hz地震噪声场中，视相速度表现出一种耗散特征，可以用瑞利波频散曲线来解释。因此，我们认为，在Kakkonda地热区观测到的地震噪声是源于储层的体波在地表附近转换而成的基模瑞利波。八里曼台热区东部震源噪声到达方向均匀，噪声源较深。在1 ~ 10hz地震噪声场中，视相速度表现出一种耗散特征，可以用瑞利波频散曲线来解释。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。

Georthermal seismic propagation at the kakkonda geothermal area and the eastern region of Hachimantai was investigated by the tripartite method and frequency-wavenumber analysis respectively. The direction of arrival and the apparent phase velocity for seismic noise from 1 to 10Hz were investigated.The conclusions may be summarized as under.1. No diurnal and secular variations of arrival direction for seismic noise at the kakkonda geothermal area are observed. Arrival quadrants obtained near the steam supply system are changed before and after the closure of wellhead valve of gerthermal prodection wells. Seismic noise in the 3-7Hz is arriving from the direction of geothermal reservoir. Apparent phase velocities for the 1-10Hz seismic noise field show the despersive characteristics and can be explained by the Rayleigh wave dispersion curve. Consequently, it is suggested that seismic noise observed in the Kakkonda geothermal area is the fundamental-mode Rayleigh waves which body waves originating at a reservoir were converted near the surface.2. Sesmic noise at the eastern region of Hachimantai geothermal area had a uniform direction of arrival and was originated from a relatively deep subterranean area. Apparent phase velocities for the 1-10Hz seismic noise field show the despersive characteristics and can be explained by the Rayleigh wave dispersion curve.Further evaluation of the effectiveness of geothermal seismic noise survey is required by accumulation of survey data at an increased number of geothermal areas.