云南地区地脉动噪声特征分析研究

对地震台站记录到的长时间背景噪声进行互相关可以得到台站间的格林函数, 进而可以对地下介质波速结构和波速变化进行研究。 对背景噪声来源方向和时空演化规律的分析, 是提高结果可靠性的重要基础。 本文利用分布在云南境内的43个宽频带固定台站2008—2010年的垂直分量记录, 计算了两两台站之间的互相关函数, 并用平均能量流的方法研究了云南地区5~10 s以及10~20 s两个频段内地脉动噪声能量的空间分布和时间演化。 研究结果表明, 云南地区5~10 s的地脉动噪声能量优势方向存在明显的季节性变化, 夏季优势能量方位角为180°~210°, 冬季则为70°~100°。 而10~20 s的地脉动噪声优势方向方位角较为稳定, 为180°~210°。 在这两个频段内噪声能量的强度都表现出了较强的季节性变化。 同时发现在5~10 s频段瑞利面波之前存在视速度接近30 km/s的前驱信号, 并对其可能来源进行了分析。

Study on the Characteristics of Microseisms in the Yunan Region,China

The Green's function between two stations can be extracted by cross correlating long time range ambient noise recorded by these stations, thus can be used for subsurface velocity inversion as well as time lapse monitoring of velocity variation. The knowledge of the variation of ambient noise direction and strength is important to improve the precision of these researches. Using the vertical component records from the Yunnan regional broadband seismic stations from 2008 to 2010, we calculated the noise cross correlation functions between each stations, then used the normalized background energy flux measurement to study the characteristicss of ambient noise in Yunan region, especially for secondary microseism period in 5~10s and primary microseism in 10~20 s. A significant direction variation of 5~10 s noise energy is observed, whose azimuth is 180°~210° in the Summer and moves to 70°~100° in the Winter. The direction of 10~20 s ambient noise is more stable covering 180°~210°. The strength of ambient noise of both types shows seasonal variation. We also observed strong near-zero arrivals with apparent velocity about 30 km/s, the possible mechanics of this precursors are discussed.