淮南深地实验室分布式光纤地震立体台阵观测数据分析

在淮南深地实验室布设了水泥固结的传感光缆,结合竖井中已有通信光缆,利用分布式光纤地震传感技术(DAS)构建了高密度的三分量立体台阵,开展了为期一年的连续观测.通过分析地下870 m的背景噪声记录,发现其日间变化幅度较小,这表明深地实验室受气压、温度和人类活动等的影响较小.然而,在低频段观测到明显增强的噪声,这给低频信号研究带来了一定困难.在连续记录中,识别出了多个地方震和区域震信号,尤其是获得了高质量的玛多地震P波信号.与共址地震仪数据的一致性表明DAS波形记录的可靠性.通过三分量DAS记录识别了Rayleigh面波信号,并利用多重滤波技术测量得到其群速度频散曲线;利用DAS应变率记录与共址宽频带地震仪的速度记录比值获得了相速度信息.两种方法测得的面波频散数据可用于研究速度结构.这些初步结果展现了深地实验室提供的超静环境以及三分量立体DAS台阵观测的优势,为后续进一步研究提供参考.

Preliminary study on data recorded by a 3D distributed acoustic sensing array in the Huainandeep underground laboratory

A three-dimensional distributed acoustic sensing (DAS) array was deployed in the Huainan deep underground laboratory, which locates at a depth of 870 m. The DAS array consists of an optic fiber cable cemented in a horizontal tunnel and an existing mine communication cable in a vertical shaft, which makes three-dimensional recording possible. Analysis on the ambient noise recorded at 870 m underground suggests that the influences of air-pressure, temperature and anthropic activities are much weaker than data recorded on surface. During the one-year observation period, signals of several earthquakes at distances from 47 to 1817 km were identified by eye-scanning. In particular, high quality P wave signal of Madoi earthquake was recorded. The strain-rate waveforms recorded by the DAS and derived from two seismometers′ records are consistent with each other, which indicates high fidelity of DAS data. Rayleigh wave signal was identified with the polarization by DAS three-component records and its group velocities were measured with the multiple-taper filtering method. On the other hand, raw records of DAS and seismometer were directly compared to estimate phase velocity. Both group and phase velocities can be used to image seismic structure beneath the site. In summary, the underground laboratory provides a unique quiet site to build 3D DAS array, which provides high-quality data for seismic imaging and monitoring.