Seismic mechanism induced by coordinated fracturing of sub-key strata under repeated mining and seismic mitigation effect of goafs

Mining-induced seismicity, a type of non-natural seismic event triggered by mining activities, poses a major threat to the safety of coal mine production due to the rapid release of elastic energy and the potential damage to underground structures and surface buildings. Focusing on a seismic event in a coal mine in Heilongjiang Province, where strong ground vibration was observed at the surface but not perceived at the working face, a combined approach of theoretical analysis, numerical simulation, and field monitoring is employed. The study analyzes the mechanism of mining-induced seismicity associated with cooperative fracture of sub-key strata in overlying goaf areas under repeated mining. A three-zone displacement mechanical model based on spring–Maxwell elements is established to represent the distinct mechanical behaviors of different overburden blocks. Multiple numerical simulation schemes are designed to comparatively investigate the propagation and attenuation characteristics of seismic wave carriers under different overburden conditions. The results show that large-scale retreat mining in the underlying working face creates new migration space for the overlying goaf, disrupting the original stress balance. Fracture of the sub-key strata in the uncollapsed roof of the original goaf then releases a large amount of accumulated elastic energy, triggering mining-induced seismicity. After seismic waves propagate through the goaf, the peak particle velocity and acceleration are attenuated by approximately 84% and 90%, respectively, compared with conditions without an overlying goaf, and both parameters approach zero at the underlying coal seam working face. These results indicate that the goaf acts as an effective buffer and energy-dissipating medium for seismic wave propagation. On this basis, a regional protective technology centered on “blasting-induced roof fracturing combined with coal seam borehole pressure relief ” is proposed to pre-fracture the hard roof and relieve stress concentration in advance. Subsequent microseismic monitoring shows that the frequency of high-energy mining-induced seismic events decreases compared with the period before implementation, and the capability for dynamic disaster prevention and control in deep mining is enhanced.