## 3 Overview and Mechanism of Mining-Induced Earthquake Events at the 3308 Working Face
### Analysis of Microseismic Activity Patterns Before and After High-Energy Mining-Induced Earthquakes  
3.1 Time-Frequency Analysis of Microseismic Activity Patterns Before and After High-Energy Mining-Induced Earthquakes  
The microseismic statistics and advance data for the 3308 working face from 25 August to 14 September are shown in Figure 9. During this period, the daily frequency of microseismic events fluctuated between 10 and 25, with maximum energy per event not exceeding 10,000 J and total energy not surpassing 40,000 J. However, on 6 September, the frequency of microseismic events surged to 32, and on 7 September it further increased to 47, with a maximum energy of 27,000 J and a total energy of 114,000 J on that day. Prior to high-energy mining-induced earthquake events, the microseismic response typically exhibits a sharp increase in frequency, with relatively low single-event and total energy levels. As a high-energy event approaches, a \"silent period\" in microseismic activity often emerges [20]. For instance, on 9 September, the frequency, maximum energy, and total energy of microseismic events all declined to low levels, indicating the imminent high-energy mining-induced earthquake event on 10 September. It is noteworthy that precursors to a high-energy mining-induced earthquake were evident in the 3308 working face prior to mining, with abnormal microseismic responses beginning on 6 September. However, the extraction advance on 8 September was only  
Figure 9: Microseismic statistics and location information of the 3308 working face (25 August–14 September). 0.8 m, suggesting a weak correlation between microseismic responses and the working face advance. The microseismic statistics and advance data for the 3308 working face from 5 December to 24 December are shown in Figure 10. During regular mining, the daily microseismic frequency at the 3308 working face ranged from 10 to 34, with total energy between 10,000 J and 38,000 J, and maximum energy per event between 3500 J and 36,000 J. On 15 December, the maximum energy per microseismic event reached 36,000 J, marking a high-energy event. On the same day, the daily advance increased from 0.3 m to 0.8 m, indirectly contributing to the high-energy mining-induced earthquake on 20 December. Additionally, a microseismic \"silent period\" was also observed during this period, further indicating the impending high-energy event on 20 December. In mining-induced earthquake prediction and prevention research, the silent period refers to a phase before a high-energy mining-induced earthquake event when the frequency and energy levels of microseismic activity decrease markedly or even temporarily cease. This phenomenon is considered a precursor signal of energy accumulation within the rock mass, manifested by relative calm in mining-induced earthquake activity, while the actual stress field continues to increase and concentrate [21; 23]. In hard roofs or rock layers, the occurrence of a silent period typically indicates an elevated risk of mining-induced earthquakes or rockbursts. Due to their high strength and low deformability, hard rock layers often do not exhibit significant deformation or fracturing during stress accumulation. As the silent period lengthens, the accumulated elastic energy grows, and upon release, may result in strong mining-induced earthquake events or even rockbursts. This phenomenon is especially common near hard roofs or large structural faults. Therefore, recognizing the silent period is crucial for mining-induced earthquake prediction. By monitoring changes in microseismic activity frequency, mines can detect the onset of a silent period and promptly implement precautionary measures, such as reducing extraction speed, reinforcing support structures, or applying preventive pressure-relief methods to mitigate potential disaster risks. In mine areas prone to high-energy mining-induced earthquake events or rockbursts, monitoring and early warning of silent periods are essential measures for ensuring mine safety.