## 4 Risk Assessment and Countermeasures for Mining-Induced Earthquake at the 3308 Working Face
### Recommendations for Mining-Induced Earthquake Prevention and Control  
Before the occurrence of high-energy mining-induced earthquake events at the 3308 working face, the Yangcheng Coal Mine implemented combined support measures including anchors, nets, cables, and belts, based on the relatively weak roof support strength to ensure that the roadway support system could withstand mining-induced earthquake events up to a magnitude of 2.48. This support system was designed to resist vibration energy of up to 3.25 \(\times\) 10\({}^{6}\) J from beyond 20 m of the roadway surrounding rock (based on calculations in the \"Anti-Burst Design for the 3308 Working Face at Yangcheng Coal Mine\"). Monitoring and early warning methods included the drill cuttings method, microseismic monitoring systems, and an online stress monitoring system for rockburst, enabling multi-level monitoring.  
For stress relief, the Yangcheng Coal Mine utilized drilling-based pressure relief, targeting low-to-moderate risk zones with large-diameter relief boreholes spaced no more than 1.6 m apart in a blanket layout during development. These boreholes were positioned between rows of anchor bolts to minimize damage to the support system. Each borehole had a diameter of 150 mm, a distance of 0.5 to 1.5 m from the floor, an angle consistent with the coal seam, and a depth of 20 m, with spacing adjusted according to site conditions.  
Following the high-energy mining-induced earthquake event, the Yangcheng Coal Mine promptly implemented additional measures, reducing borehole spacing to \"one borehole per row of bolts\" and extending the depth of sidewall boreholes to 25 m. When pressure relief was insufficient, explosives were loaded into boreholes for blasting, with deep-hole blasting directed toward the fault-protected coal pillar. This series of actions significantly reduced microseismic energy; statistics showed a marked reduction in maximum and total microseismic energy in December after the high-energy mining-induced earthquake event in September, alongside a noticeable decrease in microseismic responses.  
Based on existing control measures and this study, the following recommendations are proposed to further optimize high-energy mining-induced earthquake event control at the Yangcheng Coal Mine:  
1. Optimize sensor networks to enhance the accuracy of microseismic localization.
2. Strengthen technical training to improve the data processing skills of personnel in microseismic and stress monitoring.
3. Adjust the working face layout to avoid the influence area of fault-protected coal pillars and redesign the cutout position; consider relocating the belt roadway layout to avoid proximity to the DF56 fault.
4. Drill high-level roof boreholes toward the goaf and fault-protected coal pillar along the 3308 track roadway for pressure relief, using hydraulic fracturing and deep-hole blasting to alleviate stress in the fault-protected coal pillar while caving in the goaf area to interrupt support pressure transmission.
5. Analyze microseismic data in-depth to ensure timely responses.
6. Optimize extraction speed and recalculate support pressures, reinforcing supports if necessary.
7. Enhance support and monitoring in key management areas, implementing timely pressure relief, caving, and other measures to prevent rockburst hazards.  
These measures aim to further reduce the impact of mining-induced earthquake events on the 3308 working face, ensuring the safety and stability of the mining process. Through risk zone delineation for the 3308 working face and targeted control measures in high-risk areas, no further high-energy mining-induced earthquake events occurred at this working face from the initiation of these control measures until the end of extraction. This outcome demonstrates that the proposed risk zone delineation method and control strategy in this study effectively support safe deep coal mining and provide a sound technical and scientific basis for future mine safety.