Study On The Source Parameters And Rupture Mechanism Of Micro-earthquakes In Coal Mine

Coal and rock dynamic disasters are very serious in China.With the continuous increase of mining depth,coal and rock dynamic disasters become more and more serious and complex,which has a significant impact on the safe and efficient mining of deep resources.As a geophysical monitoring method widely used in coal mines,microseismic monitoring technology can play an important role in source location and energy analysis,evolution process of rock burst,monitoring and early warning of rock burst.However,the heterogeneity of coal-bearing strata is strong and changeable,the wave field structure is complex,the accuracy and stability of microseismic location are difficult to meet the needs of the site,and there is a lack of in-depth systematic research on the parameters of microseismic source and the mechanism of source rupture in coal mines at home and abroad.In this paper,the source parameters and characteristics,relative positioning method and source mechanism of coal mine microseisms are studied in depth by means of laboratory experiments,theoretical analysis,numerical simulation and field test verification,and the propagation characteristics of wave field under complex coal and rock medium model as the breakthrough point.The field verification and application are also carried out.The main research results are as follows:Aiming at the complex wave field structure of coal measures strata,the influence law and mechanism of complex coal and rock medium conditions on the propagation process of vibration wave are revealed.The results show that the high-order finite difference method can simulate the propagation of various waves in different coal and rock media models visually,and the shapes of reflected,transmitted and converted waves produced in different media boundary layers are different.A new source will be formed at the fault to produce refraction and diffraction waves,and slow P and S waves will be produced in biphase media.In random discrete media,more complex scattering waves will be generated.It lays a foundation for introducing the joint source location method and calculating the source parameters?especially the quality attenuation factor Q?.A simplex and double difference combined location method is proposed to correct the location of microseismic source in coal mine site,which improves the accuracy of source location.The results show that the source location error of blasting events given by simplex and double-difference joint positioning method is controlled within20 m,and the residual error of events is controlled within 15 ms,which verifies the accuracy of the joint positioning method.The root-mean-square residuals of coal mine microseismic events are reduced from 1.35s to 0.62s by joint positioning method,and the accuracy of source location is improved obviously.This method effectively reduces the errors caused by the inaccuracy of crustal velocity structure model,and ensures the accuracy of source location and source parameters.Based on the?² model,the source parameters?corner frequency f₀,quality attenuation factor Q,source energy E,seismic moment M₀,source radius R,stress drop??,apparent stress?_a?and magnitude of laboratory small scale coal and rock rupture and coal mine microseism are accurately determined.The results show that the source parameters f₀ and?_a of small-scale coal and rock samples in laboratory decrease linearly with the increase of M₀,and the source parameters R and E increase linearly with the increase of M₀,the fluctuates around a certain value on the whole.In Laohutai Coal Mine,the source parameters f₀ of the micro-earthquake decrease linearly with the increase of M₀,while the source parameters R,E and??increase linearly with the increase of M₀.However,the linear relationship between??and M₀is weak,and?_a fluctuates almost around a certain value.Moreover,the values of f₀and??of the microseismic in Laohutai Coal Mine are obviously smaller than those of the source parameters corresponding to natural earthquakes.The source rupture mechanism,rupture scale and slip distribution on rupture surface of small scale rupture and coal mine microseism are studied,and the source rupture mechanism is revealed.The results show that the source beach ball inverted by moment tensor inversion method can clearly distinguish the characteristics of shear failure,shear tension failure and shear compression failure existing in small-scale rupture and coal mine microseismic source rupture.According to the relationship between source rupture scale and moment magnitude,the rupture area,length,width and slip of the source are calculated,and the rupture range of the source is evaluated systematically.Based on the calculated rupture scale and K² slip rupture model,the source slip distribution of different magnitude rupture events is obtained,and the source slip rupture process is revealed.A software for inversion of source parameters and analysis of source rupture mechanism of microseisms is developed,which realizes automatic processing,location calculation,inversion of source parameters and analysis of source rupture mechanism of microseisms monitoring waveform data.The characteristics and mechanism of source parameters of rock burst damage in Qianqiu Coal Mine are revealed.The focal rupture scale and slip distribution data of four rock burst events are obtained,and the results are basically consistent with the actual situation in the field.It is revealed that the area with large sliding on the rupture surface of mine quake is easy to induce rock burst,therefore,based on the slip distribution on the rupture surface,effective regional prevention and control of rock burst can be carried out.The research results have important theoretical significance and application value for further improving the accuracy of micro-seismic source location in coal mine,revealing the rupture mechanism of earthquake shocks and rock burst disasters,accurately evaluating and predicting rock burst,and effectively preventing rock burst disasters.