千秋煤矿微震震源参数特征以及震源机制分析

为了解释和量化采矿诱发微震的危险性,提高采矿作业安全性,首先基于Brune模型和网格搜索法,求取千秋煤矿微震的地震矩、拐角频率、震源半径和应力降等震源参数以及矩震级,分析震源参数与矩震级之间的关系,最后基于震源参数和P波反演法来反演震源机制解。研究结果表明:①千秋煤矿微震震源位移谱很好地符合Brune模型,基于此通过网格搜索法可以迅速准确地求取震源的拐角频率f_c和拐角谱值Ω_c;②基于拐角频率f_c和拐角谱值Ω_c和相关的理论公式,可以进一步迅速准确地求取各个震源参数和矩震级;③随着矩震级增加,拐角频率呈线性减小趋势,震源半径和应力降都呈线性增加趋势。在同等震级条件下,该矿微震的拐角频率和应力降的值都要小于天然地震,表明该矿微震的破裂尺度和形式不同于天然地震;④应用P波反演法很好地反演出了千秋煤矿的剪切破坏、剪切张拉破坏和剪切挤压破坏震源机制。千秋煤矿开采活动会引起地质不连续面的滑动,产生区域内的动载荷作用,对自由面附近的节理面产生推动作用,从而造成岩体破坏,由于巨厚砾岩层顶板容易积聚大量弹性能,岩体破坏时会产生很大的冲击。上述成果可以在震后迅速准确地量化和评估震源破裂的尺度和机制,而且根据不同震级对应震源参数的范围,可以对将要发生微震的震源参数进行迅速评估,为进一步研究矿山微震震源的破裂过程和危险性的评估提供借鉴。

Analysis of microseismic source parameters and focal mechanism in Qianqiu Coal Mine

Seismicity related to mining activities poses a man made (induced) seismic hazard that needs to be understood and quantified in order to ensure safe mining operations.In this paper,based on the Brune model and the grid search method,the authors firstly obtain the seismic moment,corner frequency,source radius and stress drop,and the moment magnitude.Then the relationship between the source parameters and moment magnitude is analyzed.Finally,the focal mechanism is derived based on the source parameters and the P wave inversion method.The results show that:① The source displacement spectrum of micro earthquakes in Qianqiu Coal Mine fits well with the Brune model.Based on this,the corner frequency fc and corner spectral Ωc of seismic source can be quickly and accurately calculated by grid search method;② Based on corner frequency fc,corner spectral Ωc and related theoretical formulas,the source parameters and moment magnitudes can be obtained more quickly and accurately;③ With the increase of moment magnitude,the corner frequency decreases linearly,the source radius and stress drop increase linearly.Under the same magnitude condition,the corner frequency and stress drop of the mine are smaller than those of natural earthquakes,indicating that the rupture form of mine micro earthquake is different from that of natural earthquake;④ The P wave inversion method can well be used to reverse the focal mechanism shear failure,shear tension and shear compression failure of micro earthquakes in Qianqiu Coal Mine.The mining activity of Qianqiu Coal Mine will cause the sliding of geological discontinuity surface,generate dynamic load in the area,and promote the joint surface near the free surface,thus causing rock mass damage.Because the roof of the thick conglomerate stratum is easy to accumulate a large amount of elastic energy,the rock mass will have a big impact when it is destroyed.These results can quantify and evaluate the scale and mechanism of focal rupture quickly and accurately after an earthquake.Furthermore,according to the range of focal parameters corresponding to different magnitudes,the source parameters of forthcoming microseisms can be rapidly evaluated.All these have laid the foundation for further research on the rupture mechanism and prediction of microseism.