利用地震背景噪声提取西山村滑坡高频面波信号

滑坡体三维速度结构为滑坡治理、灾害防治、风险防范以及理解滑坡的动力学过程提供了关键信息,而高频面波成像是研究浅层速度结构的重要手段.本文详细介绍了利用2016年12月1日在四川理县西山村滑坡上布设的38个仪器记录的三分量连续地震噪声数据,提取1～5Hz的基阶Love波和Rayleigh波经验格林函数,分析了不同参数和处理方法对背景噪声互相关计算结果的影响.结果表明,1天左右的连续波形记录裁剪至1200s的时间长度,进行互相关叠加就可以得到较为稳定的经验格林函数.西山村滑坡体上Love波和Rayleigh波的群速度分别为约400m·s-1和700m·s-1,并且Love波信噪比高于Rayleigh波.此外,我们还利用聚束分析方法对噪声源的位置进行了分析,发现1～5Hz的背景噪声主要来自滑坡东南侧附近杂谷脑河水的搬运作用.这些高频面波数据和噪声源位置为获取滑坡浅层三维速度结构提供了重要输入,同时也为研究滑坡体速度结构随时间的变化提供了基础.

Extraction of high-frequency surface waves on the Xishancun landslide from ambient seismic noises

Three-dimensional structures of landslides provide key information to landslide treatment, disaster prevention, and risk mitigation, as well as the understanding of landslide dynamics, while high-frequency surface wave tomography has been proven to be an effective method to image shallow structures. In this study, we attempt to obtain high-frequency surface waves for 38 stations on the Xishancun landslide in southwestern China. We extract empirical Green's functions from three-component continuous ambient seismic noises recorded on December 1^st, 2016. First, we test several parameters that may yield better noise correlation functions (NCFs), including time-segment length, data filtering, and topography effect. After stacking NCFs from one-day noises with a segment length of 1200 s, we obtain clear Love and Rayleigh waves in the frequency range of 1~5 Hz with apparent velocities at about 400 m·s^-1 and 700 m·s^-1, respectively. Love waves generally have higher signal-to-noise ratios than Rayleigh waves. Beamforming of Love waves suggests that the seismic noises mainly come from the sediment transport of the river to the south toe of the landslide. The obtained surface waves and location of seismic noises provide a valuable input for 3D tomography of the shallow structures of the Xishancun landslide, as well as their temporal variations.