普洱大寨深井噪声压制效果及井孔附近波场特征研究

Ability of decreasing noise and the characteristics of nearsurface wave field around Dazhai borehole in Pu'er

  • 摘要: 基于2011年建立的云南普洱大寨深井台站,开展了噪声压制及附近波场特征研究.通过计算该台站的噪声功率谱概率密度函数,显示该井下台站对1 Hz以上的高频噪声具有明显的压制效果, 最高能降低40 dB,其降噪能力优于其它井下台阵,推断与该台站附近的场地条件有关.基于地表与井下地震记录的差异,应用正则化反卷积干涉方法进一步研究该台站附近的波场特征.以地表记录为参考,对井下记录进行反卷积,获取两台站之间的格林函数,直接识别出了原始记录上无法区分的上行入射波与下行地表反射波,然后利用两震相的到时差建立了一个浅层地震波速度模型,与理论模拟的结果一致.研究结果表明,相对于地表观测,井下台站在压制噪声和近地表地震波传播特征研究等方面具有很大的优势,同时该研究对其它地区开展深井观测具有参考意义.

     

    Abstract: In 2011, the Dazhai borebole station was established in Pu'er, Yunnan Province, to carry out some researches on noise suppression and the wavefield characteristics. We compute the power spectral density of continuous noise recordings within ten months to quantify the reduction in seismic noise with the station depth. The results demonstrate that the downhole station has obvious effect on decreasing noise up to 40 dB within the frequency band more than 1 Hz, which might be associated with the local site conditions. The Green's functions are then obtained between the two receivers by deconvoluting the down-hole recordings with the surface ones. From the deconvolution wavefield, the arrivals of up-going incident and down-going surface-reflection waves are directly identified that cannot be distinguished from the original seismic recordings. The two phases are utilized to set up a shallow seismic wave velocity model, which is consistent with the theoretical results. A comparison with the surface observation suggests that the borehole stations have great advantages in reducing noise and studying the propagation characteristics of near-surface seismic waves. The research here is of great significance for future down-hole observations in other sites.

     

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