Study on Characteristics of Geothermal Seismic Noise by Array Observation

分别用三分法和频率-波数分析方法研究了卡孔达地热区和哈奇曼台东部地区的温差地震传播。研究了1~10赫兹地震噪声的波达方向和视相速度。在Kakkonda地热区没有观测到地震噪声到达方向的日变化和长期变化。地热探井关闭井口阀门前后，在蒸汽供应系统附近得到的到达象限发生了变化。3-7赫兹的地震噪声来自地热藏方向。1-10赫兹地震噪声场的视相速度表现出弥散特征，可以用瑞利波频散曲线来解释。因此，在Kakkonda地热区观测到的地震噪声是起源于储集层的体波在地表附近转换而成的基模瑞利波。哈赤曼台地热区东部地区的地震噪声具有一致的到达方向，来自较深的地下区域。1-10 Hz地震噪声场的视相速度表现出弥散特征，可以用瑞利波频散曲线来解释。地热地震噪声调查的有效性需要在越来越多的地热区积累调查数据来进一步评价。

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.