Numerical simulation study on sub-regional evolution of microseismic characteristics of mining overburden rock

In order to explore the fracture zone characteristics and microseismic evolution within overburden rock above mining coal seam, based on the geological engineering conditions of a mine, a microseismic simulation method was constructed according to the moment tensor and particle flow theory, and the microseismic evolution characteristics of overburden rock above panels were simulated. The results show that the magnitude of microseismic events in mining-disturbed overburden is between −2.7 and −1, and the microseismic fracture strength conforms to the Gaussian distribution. The relationship between microseismic frequency and moment magnitude also satisfies the classical moment magnitude-frequency relationship. The microseismic events show prominent regional distribution characteristics in the horizontal direction of the panel. The microseismic events in the left and right coal walls of the goaf occur earlier than the roof above goaf, and the microseismic events develop to both sides around the mining space, and there is a certain advance and lag. When the panel is mined for a certain distance, the vertical stress of the overburden above the goaf shows a 'double peak' characteristic, and the microseismic events extend upward rapidly and gather and develop in the weak overburden so that the microseismic events also show prominent layered distribution characteristics in the vertical direction. According to the stress, displacement, and microseismic distribution characteristics within overburden, the overburden can be divided into ‘four horizontal zones’ and ‘three vertical zones’. The proportion of microseismic events and fracture types in each fracture area is different. The coal wall supported and bed separation areas are the large proportion areas of shear and tensile microseismic events, respectively. In addition, a microseismic monitoring system was established for the study area. The field monitoring and numerical simulation results are consistent, indicating that the constructed microseismic simulation method has a good applicability and can reproduce the microseismic evolution process of mining-disturbed overburden from the mesoscopic level. The research results provide a theoretical basis for revealing the evolution mechanism of mining-induced fractures.