## 2 Engineering Background  
The depth of the 501 working face in the TB coal mine is approximately 500 m, with a dip length of 203 m and a strike length of 1103 m. It mines the M4-5 coal seam, with an average thickness and dip angle of 9 m and 18\({}^{\circ}\), respectively. A 412 gob exists around the 501 working face, with a 40 m coal pillar separating the working face from the gob.  
The 501 working face exposed 28 faults during mining, including 5 penetrating faults. Taking the T6 penetrating fault as an example, it had a dip angle of 75\({}^{\circ}\) and a drop of 2 m. The extension length of the penetrating T6 fault was significant, and its azimuth angle was 53\({}^{\circ}\), bisecting the 510 working face in the dip direction, resulting in the formation of a triangular coal pillar with an included angle of 37\({}^{\circ}\), as shown in Figure 1.  
From 8 March 2021 to 7 April 2021, as the 501 working face was excavated 200 m away from the T6 penetrating fault, the energy and frequency of microseismic increased significantly, mainly concentrated in three areas: the 501 working face, the T6 and T5 penetrating faults, and the triangular coal pillar (as shown in Figure 2a). The analysis of the microseismic concentration area is presented in Figure 2b by quantifying the distribution of microseismic strike directions with step of 20 m.  
Figure 1: Triangular coal pillar position of 501 working face.  
The support of the 501 working face roadway employs a combination of bolts and cables. The specifications for the bolts in the roof are \(\varphi\)22 mm \(\times\) 2400 mm, with a row spacing of 1200 mm and a column spacing of 1000 mm. For the cables in the roof, the parameters are a diameter of 21.8 mm and a length of 7300 mm, with rows spaced at 1800 mm and columns spaced at 1000 m. Additionally, the parameters for the bolts in the walls of the roadway are \(\varphi\)22 mm \(\times\) 2400 mm, with a row spacing of 800 mm and a column spacing of 1000 mm.  
As the working face approached the fault, significant deformation was observed in both the roof and the walls of the roadway. Consequently, reinforcement measures were introduced by adding cables to the roof and walls of the roadway. Specifically, the roof reinforcement cables were upgraded to \(\varphi\)21.8 mm \(\times\) 9300 mm, with two additional cables per row installed. Furthermore, the reinforcement for the walls of the roadway involved adding cables with a diameter of 21.8 mm and a length of 4300 mm, with one additional cable added every two rows.  
Given the relatively intact condition of the on-site roof and walls of the roadway, rock mass injection measures were deemed unnecessary.  
Area 1-501 working face: the microseismic energy and frequency were 1 \(\times\) 10\({}^{5}\) J and 143, respectively, which are at a high level. Using the key stratum theory [60, 61] to identify borehole 42-6, a sub key stratum of coarse sandstone with thickness of 37.18 m existed 30 m above the 501 working face, as shown in Figure 3. The breakage of the key stratum [62, 63] caused the concentration of microseisms within 40 m around the working face.  
Area 2-T6 and T5 penetrating fault: the fault was activated by abutment stress 200 m ahead of the working face [13, 29]. Microseismic events were concentrated in 60 m around the T6 and T5 penetrating faults, and the maximum accumulated energy ranged from 1.11 \(\times\) 10\({}^{5}\)-1.36 \(\times\) 10\({}^{5}\).  
In Area 3, the width of the triangular coal pillar was 200 m. The overall microseismic frequency and energy of the triangular coal pillar was 74.8% and 70.2% of the entire working face, respectively, indicating a high-level stress throughout the coal pillar. Additionally, the stress evolution in this area was intricate due to the varying width of the coal pillar.  
Figure 2: Microseismic distribution from 501 working face excavation to fault. (**a**) plane distribution of microseisms. (**b**) strike distribution of microseisms.