Temporal-spatial characterization of mining-induced seismicity in the vicinity of a dyke – A case study

Abstract

Major faults and dykes are common geological discontinuities in underground mines and can often contribute to significant failures such as coal bursts during mining. The failure mechanisms of faults have been widely studied, whereas the seismic characteristics associated with dykes have been rarely investigated for mine dynamic hazard risk management. This research aimed to characterize the seismic behavior near an intrusive dyke that intersected with the roadways in an underground longwall coal mine in Australia. The temporal-spatial variations of seismic multi-parameters around the stiff dyke were analyzed, including clustered seismicity, event locations, Es/Ep ratio, b-value and correlation with the released seismic energy. Four stages were defined based on the evolutions of seismic characteristics. The rock fractures initiated near the dyke when the longwall face was 400 m from the dyke. The seismicity started to increase when the longwall was <100 m from the dyke and decreased drastically after the longwall mined 50 m past the dyke. The seismic events were concentrated at the inbye side of the dyke and propagated to the outbye side of the dyke as the longwall mined through the dyke. The spatial distribution of Es/Ep ratios and temporal variations of the b-value indicated that higher magnitude seismic events dominated by shear failures occurred in the hanging wall of the dyke, suggesting more sudden seismic energy release and escalating seismic risks around the roadways at the inbye side of the dyke. Meanwhile, when the longwall was mining through the dyke, even though the seismicity was intensive, seismic energy was more frequently and gently released so that stress was not significantly accumulated to induce any major failures at the outbye side of the dyke. The results demonstrated that the geological features of the dyke and the longwall mining progress had a controlling effect on the seismic characteristics in the time-space domain. The comprehensive analysis of seismic multi-parameters reliably revealed the rock mass response near a major dyke and can provide guidance for assessing and managing the risks of dynamic mining hazards around dykes.