## 3 Experimental Results
### Coal Mine Tremors and Prevention Cases  
Coal mine MKQ is located in the Inner Mongolia Autonomous Region, China. On 8 April 2018, a mining tremor with a magnitude of M\({}_{\text{L}}\) 2.5 occurred on working face 3102, and the ARANMISranmis microseismic monitoring system detected an energy of \(3.3\times 10^{7}\) J. The tremor source was located 71 m above the coal seam, near the interface  
Figure 16: The process of mine tremor occurrence in a thick hard sandstone roof: (**a**) bending and sinking of the sandstone layers; (**b**) interfacial shear slips due to the bending of sandstone layers; (**c**) fracturing of the sandstone layers; and (**d**) interfacial shear slips promoted by fracturing of the sandstone layers. between the 31 m-thick coarse-grained sandstone and the 28.9 m-thick medium-grained sandstone above it. The workers underground heard two consecutive heavy and dull sounds from the roof, and there was a significant vibration sensed on the surface. As shown in Figure 17, this mine tremor caused serious damage to 114 m of roadways and minor damage to 186 m of roadways. The support system was severely damaged, and production on the working face had to be stopped. The microseismic waveform of the tremor is shown in Figure 18. The proportion of the transverse waves of this mining tremor was higher than that of the longitudinal waves, and the duration and magnitude of the tremor were higher than those caused by the tensile fracturing of the roof of the ordinary goat. This was the primary cause of the obvious ground shaking. The main frequency of the waveform of this mining tremor event was 0.73-7.43 Hz, with an average of 2.26 Hz. The wavelength was 498-5299 m, with an average of 3156 m. The waveform duration was 1.55-4.95 s. The source exhibited a shear-tension mixed-fracturing form dominated by shear fracturing. Thus, it is inferred that the shear fractures were likely caused by a shear slip failure between the coarse-grained sandstone and medium-grained sandstone layers. Figure 17: Location of mining tremor source and damage to a roadway. Figure 18: Waveforms of the mine tremor monitored by different seismometers. It is clear that the closer the source of the mining tremor is to the coal seam, the more likely it is to transition from a non-hazardous mining tremor to a hazardous one. For hazardous mining tremors, preventive measures must be taken to protect the safety of the roadway. For a mining tremor involving layered rock strata, we should try to implement measures to avoid the simultaneous fracturing of the upper and lower layers of sandstone and to reduce the interlayer shear slip behaviors to reduce the energy release and duration of the mining tremor and, ultimately, reduce the damage to the underground roadway. In order to avoid mining working faces from experiencing hazardous mining tremors, for working face 3106 in the same mining area, special blasting measures were designed for the roof. The layout of the blasting holes is shown in Figure 19.  
Taking coal seam 2-2 as a dividing line, the 0-115 m-thick strata above coal seam 3-1 are divided into the low-level rock strata and medium-level rock strata. For the low-level rock strata, a set of fan-shaped roof blasting holes are arranged every 20 m, including hole numbers A-1 and A-2. The angles between these holes and the coal seam are 60\({}^{\circ}\) and 45\({}^{\circ}\), respectively, and the depths of these holes are 31 m and 38 m. The diameters of the holes are 89 mm. The purpose is to completely cut off rock strata 4 and 5 along the direction of the roadway in order to avoid the danger of coalbursts caused by the fracturing of hard stratum 4. For the medium-level rock mass, a set of longer fan-shaped roof blasting holes are arranged every 100 m, including hole numbers B-1 and B-2. The angles between these holes and the coal seam are 60 and 47\({}^{\circ}\), respectively, and the depths of these holes are 89 and 101 m. The diameters of these holes are 75 mm.