Applicability of an imaging method for ambient noise in coal mines based on triangular and linear arrays
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摘要: 背景噪声面波成像在大尺度区域构造及浅层工程勘探中已得到广泛应用,但在几百米至1 km深度范围内探测研究相对较少。该探测深度利用的噪声源为几赫兹至十几赫兹的人文环境噪声,在时间空间上变化较大。为研究背景噪声成像技术在煤矿尺度探测中的适用性,本文以里必煤矿深部探测为例,通过实验数据系统分析了噪声源的分布特征及不同台阵频散成像的适应性。研究发现,矿区2 Hz以下噪声能量在晚上占主导,大于2 Hz噪声源能量在白天占主导;目标3号煤层埋深(700 m)利用的噪声频段(2~10 Hz)主要分布在东南方向;当噪声源能量和方位相对单一时,与噪声源方向一致的线性台阵可以获得比三角形台阵更好的频散数据。最后,通过提取NW向线性台阵的频散数据,获得了台阵下方的一维速度结构。与台阵附近ZK101钻孔岩性柱状图对比分析,得出利用背景噪声成像获得的速度结构与地下岩性具有较好的对应关系。说明在充分考虑噪声源分布的情况下,基于线性台阵的背景噪声成像可以获得煤矿尺度1 km以浅可靠的速度结构。Abstract: Ambient noise surface wave imaging has been widely applied in the engineering exploration of large-scale regional structures and shallow parts. However, there are limited studies on the exploration of mineral resources at depths ranging from several hundreds of meters to one kilometer. The noise source utilized for exploration at this depth range is human environmental noise with frequencies from a few Hz to over ten Hz, varying greatly in time and space. To examine the applicability of ambient noise imaging in the exploration of coal mines, this study systematically analyzed noise source distribution and the adaptability of various array dispersion imaging schemes using experimental data from the Libi Coal Mine. As revealed by the results, the noise in the coal mine is dominated by that with frequencies below 2Hz at night and by that above 2Hz during the day. The noise frequency band (2~10 Hz) utilized for the No. 3 coal seam at a depth of 700m is primarily distributed in the southeast. In the case of simple frequencies and azimuths of the noise sources, a linear array in the noise source direction can obtain dispersion data with higher quality than a triangular array. Finally, by extracting dispersion data from a linear array in the NW direction, the 1D velocity structure below the linear array was obtained. By comparison with the lithology column of borehole ZK101 near the linear array, the 1D velocity structure, obtained through ambient noise imaging, corresponded well with the underground lithology. This result indicates that when fully considering noise distribution, the ambient noise imaging based on a linear array can yield reliable velocity structures for layers at depths less than 1 km in a coal mine.
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