## 6 Conclusions  
The most common stratum of the roof in Ordos mining area is super-thick strata, and the fractures or slips of super-thick strata can easily trigger SMT. Field observations, numerical analysis, and theoretical calculations were used to study the mechanism of induced SMT caused by fractures in the super-thick strata in the Ordos mining area. The conclusions are as follows:  
Figure 15: Occurrence mechanism of SMT before and after goaf mining in LW 1208. (**a**) Cracks spread and subside rapidly; (**b**) Fracture and instability of super-thick strata; (**c**) Super-thick strata slip and stagger; (**d**) Super-thick strata tensile fracture.  
1. The SMTs induced by the fracture of super-thick strata are more likely to cause ground shaking. The SMTs are all located in the super-thick strata behind the goat, which is relatively close to the ground. The apparent volume distribution is more than 10\({}^{7}\) m\({}^{3}\), and the stress drop and apparent stress at the source are more than 10\({}^{4}\) Pa, which is one to three orders of magnitude higher than other mining tremors.
2. The SMTs were mainly caused by the movement of fractures in the super-thick strata. When solid coal mining was conducted, the surface subsidence was relatively small, and there were no fractures in the super-thick strata, thus SMTs did not occur. However, during goat mining, there were two \"stepped\" increases in maximum surface subsidence, and fractures began to appear in the super-thick strata, leading to the occurrence of SMTs.
3. Theoretical calculations show that, during goat mining, when LW 1208 advances by about 307 m, the super-thick strata will experience initial fracture. Then, when LW 1208 continues to advance approximately 118 m, there will be another fracture of the super-thick strata--a periodic fracture. This is the main reason for triggering the \"8.20\" and \"12.20\" SMT events. Moreover, after the super-thick strata are fractured, unstable structural adjustments can easily induce SMTs, such as the \"8.29\" SMT.
4. The strata below the super-thick strata gradually break upwards. Once the super-thick strata reach their fracture limit, it produces initial and periodic fractures in the form of tensional rupture, which can trigger SMT. Similarly, after tensional rupture occurs in the super-thick strata, the structural adjustment of the ruptured super-thick strata can produce shear failures that trigger SMTs.  
Conceptualization, Y.Y. and A.C.; methodology, Y.Y.; software, Y.L.; validation, Y.Y. and X.B.; formal analysis, Y.Y.; investigation, C.W. and A.C.; resources, S.W.; data curation, X.B. and Z.Y.; writing--original draft preparation, Y.Y.; writing--review and editing, A.C.; supervision, A.C.; project administration, A.C.; funding acquisition, A.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National key research and development program (2022 YFC3004603) and National Natural Science Foundation of China (52274098, U21A20110).  
Not applicable.  
The data used to support the findings of this study are available from the corresponding author upon request.  
The authors are grateful to Shilawusu Coal Mine for providing field testing. The authors would also like to thank the peer reviewers and Editors for their valuable comments and suggestions, which have greatly improved the manuscript presentation.  
The authors declare no conflict of interest.