基于地震和重力观测的深地超宽频带背景噪声初探

深部地下环境的"超静"特点对认识地球内部结构及演变规律具有重要意义.联合淮南深地实验室宽频带地震仪与弹簧重力仪观测资料，利用两种仪器的频率互补优势，初次探究了实验室地表与地下（-848 m）超宽频带（0.0001~50 Hz）的背景噪声水平.研究结果表明，除0.01~0.1 Hz频带内可能由于巷道内的空气流动导致地下噪声高于地表外，其余频带范围地下噪声均低于地表观测，且低频段（0.0001~0.01 Hz）差异较小而高频段（0.1~50 Hz）差异显著.此外，地下地震仪检测到更高信噪比的地球自由振荡简正振型，进一步验证了深部地下环境的"超静"特点.由于淮南深地实验室尚处于基础建设阶段，因此深部地下观测环境的"超静"特点有望随着观测条件的完善更加突显，实验结果可为深地实验室的后续建设和相关地学研究提供重要参考.

A preliminary study on the ultra-wide band ambient noise of the deep underground based on observations of the seismometer and gravimeter

The "ultra-silent" characteristic of deep underground environment is essential for understanding the internal structure and evolution of the Earth. Jointly using the observations of a broadband seismometer and a gravimeter at the Huainan Deep Underground Laboratory (HDUL), and taking advantage of their frequency complementarity, surface and underground (-848 m) ambient noise levels in the ultra-wide frequency band (0.0001~50 Hz) are preliminarily investigated. Numerical results show that the underground ambient noise level is lower than the surface noise level in most bands, and the difference between them is smaller in the low-frequency band (0.0001~0.01 Hz) while larger in the high-frequency band (0.1~50 Hz). But for the frequency band 0.01~0.1 Hz, the underground ambient noise level is higher than the surface noise level, which is most possibly caused by air flow in the coal mine roadway. In addition, higher signal-to-noise ratio free oscillation normal modes are obtained in the underground roadway, which further demonstrates the "ultra-silent" characteristic of deep underground environment. Because the HDUL is in the stage of infrastructure construction, the "ultra-silent" characteristic of deep underground environment is expected to be more prominent with the improvement of observation conditions. The results provide valuable reference for the subsequent construction of the HDUL and for related geoscience studies.