## 4 Rupture Mechanism of Strong Mining Tremors
### Rupture Mechanism of Strong Mining Tremors  
After the occurrence of an SMT, its vibration information is detected by microseismic sensors arranged near LW 1208. Figure 13 shows the seismic waveforms of the \"8.20\", \"8.29\", and \"12.20\" SMTs. The energy ratio (E\({}_{\text{S}}\)/E\({}_{\text{P}}\)) of the S-wave and P-wave of SMTs is calculated [38]. The E\({}_{\text{S}}\)/E\({}_{\text{P}}\) values of the \"8.20\", \"8.29\", and \"12.20\" SMTs are 5.24, 16.37, and 8.62, respectively. The SMTs are clearly related to tensile failure of the super-thick strata, which is consistent with the results of the above research. The focal mechanism results of the \"8.20\", \"8.29\", and \"12.20\" SMTs are shown in Table 3. It can be concluded from them that:  
Figure 13: (**a**) Vibration waves of the “8.20” SMT; (**b**) Vibration waves of the “8.29” SMT; (**c**) Vibration waves of the “12.20” SMT. For the \"8.20\" SMT, the \(P_{\text{ISO}}\), \(P_{\text{CLVD}}\), and \(P_{\text{DC}}\) were 6.37%, 74.02%, and 19.61%, respectively. The source rupture type is pure tensile failure, indicating that the \"8.20\" SMT was induced by the tensile failure of the super-thick strata. 2. For the \"8.29\" SMT, the \(P_{\text{ISO}}=-2.87\%\), \(P_{\text{CLVD}}=-22.86\%\), and \(P_{\text{DC}}=74.27\%\). The source rupture type of this SMT is shear fracture. It can be inferred that the \"8.29\" SMT is related to the slip and dislocation of the super-thick strata. It is worth noting that the disturbance caused by the \"8.20\" SMT is the key factor causing the dislocation of the super-thick strata. 3. Similar to the \"8.20\" SMT, the \(P_{\text{ISO}}\), \(P_{\text{CLVD}}\) and \(P_{\text{DC}}\) of the \"12.20\" SMT were 12.62%, 60.44% and 26.94%, respectively, which was again induced by the tensile failure of the super-thick strata. Before the SMT occurs, the layer underneath the super-thick layers breaks upwards step by step, resulting in a mining tremor. The focal mechanism of these mining tremors is solved one by one, and the evolution characteristics of the rupture mode of the source are analyzed to reveal the occurrence mechanism of the SMT. According to the different mining conditions, the mining process of LW 1208 is divided into three stages, corresponding to the solid coal mining stage and the goat mining stage, respectively. The focal mechanism of the SMT is directly represented by a diamond graph (as shown in Figure 14) [39]. At the mining stage of solid coal, the ratio of seismic numbers of different fracture types is: pure tension: pure shear: pure compression: shear-tension: shear-compression = 7:7:15:53 (seen in Figure 14a). Obviously, pure tension, pure shear, and pure compression are the main types of fracture mechanism source. The primary rupture of the roof is the main reason for the occurrence of tensile rupture mining tremors. Because of the small mined-out area and the limited roof fracture space, the roof compression failure constantly induces compressive fracture mining tremors. Under the influence of mining, the staggered instability of unstable roof blocks induces a series of shear fracture mining tremors. Until the occurrence of the \"8.20\" and \"8.29\" SMTs, a total of 28 mining tremors were induced by the mining, which five and three of which occurred in June and July 2021, respectively. All of them were distributed in the peripheral area of LW 1208, indicating that the roof movement gradually relaxed while the internal elastic energy accumulated rapidly. In August 2021, there were a total of 20 mining tremors, including two SMTs. The source fracture types of mining tremors were mainly pure tensile and pure compression fractures. It was evident that the roof strata were gradually fracturing and the elasticity was rapidly released, eventually inducing the \"8.20\" SMT. Meanwhile, under the disturbance of the \"8.20\" SMT, the rock strata became unstable again, thus inducing the \"8.29\" SMT.