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 under- stood 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 fc and corner spectral Ωc of seismic source can be quickly and accurately calculat- ed by grid search method;② Based on corner frequency fc ,corner spectral Ωc and related theoretical formulas,the source parameters and moment magnitudes can be obtained more quickly and accurately;③ With the increase of mo- ment 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 earth- quakes,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 compres- sion failure of micro-earthquakes in Qianqiu Coal Mine. The mining activity of Qianqiu Coal Mine will cause the slid- ing 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,ac- cording 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.