地面与地下深部地震背景噪声对比分析

Comparative analysis of surface and deep underground seismic ambient noise

深部地下空间具有低于地面的噪声环境,为开展高精度多物理场观测提供了绝佳平台.通过淮南潘一东矿区海拔-848 m的井下巷道和地面的地震联测,我们分析了深部地下与地面的地振动背景噪声特征.对比结果显示,大于1.0 Hz的高频段,地面噪声功率谱密度(Power Spectral Density,PSD)值高出地下20~40 dB,并呈现随人类活动变化的昼夜模式;而井下观测不存在这一时变规律,地下巷道上覆870 m厚的沉积层有效衰减了浅层或地表的人文噪声.0.1~1.0 Hz频段二者差异相对减小,地面PSD值平均高出地下10 dB.小于0.1 Hz的低频噪声差异较小,或与井下气流干扰和仪器本底噪声有关.在第二地脉动谱的对比中,可发现明显的场地放大效应和地脉动峰的分裂现象.此外,深部地下低噪声环境突显了若干高频非时变信号,根据频域极化分析可厘定这些稳定噪声为井下的固定振动源.上述结果说明深部地下可以为高精度地震观测和震源定位提供优良环境,同时也给深地实验室的后续建设以及相关深地研究提供重要参考.

Deep underground spaces have a noise environment lower than the surface,providing an excellent platform for high-precision and multi-physical fields observation.By conducting a joint seismic observation of the underground roadway at-848 meters below sea level and the surface in the Panyidong mining field in Huainan,Anhui Province of China,we analyzed their characteristics of the ambient vibrations.The comparison results reveal that the Power Spectral Density(PSD)value of noise records at the surface above 1.0 Hz is 20~40 dB higher than that at the deep underground.Moreover,a day-night pattern variation with respect to human activities is observed at the surface.In contrast,the underground records do not exhibit this time-varying phenomenon,which can be attributed to attenuation of the 870 m thick sedimentation overlying the underground roadway.In the 0.1~1.0 Hz frequency band,the difference between the surface and deep underground is relatively reduced,with a power gap of 10 dB.The difference of low frequency noises below 0.1 Hz is small,possibly due to the interference of downhole airflow and the instrument background noise.When comparing the Double-Frequency(DF)microseism spectrum,the site amplification effect and the splitting of DF microseism peak are clearly observed.Additionally,the deep underground's low-noise environment highlights several high-frequency time-invariant signals,which can be identified as equipment-induced vibrating sources through polarization analysis in frequency domain.Overall,our results confirm that the deep underground provides an excellent environment for high-precision seismic observation and source location.This study also provides an important reference for the subsequent construction of deep underground laboratory and related researches.