## 3 Overview and Mechanism of Mining-Induced Earthquake Events at the 3308 Working Face
### Analysis of the Mechanism of High-Energy Mining-Induced Earthquake Events  
(1) For the high-energy mining-induced earthquake event on 10 September:  
Stress Analysis: Prior to the 10 September high-energy mining-induced earthquake event, there was a significant increase in stress on the track roadway side of the 3308 working face, which decreased following the event. However, stress on the belt roadway side increased after the event, which does not align with the typical pattern of high-energy events occurring within the working face and its roof or floor. This indicates that the seismic event did not occur within the working face itself. Microseismic Statistical Analysis: From a microseismic perspective, the frequency of microseismic events surged on 6 September, accompanied by abnormal stress readings. Between 6 and 8 September, there was a marked increase in microseismic frequency, followed by a \"silent period\" on 9 September. Additionally, Sensor 28 on the track roadway side showed a sudden drop in stress on 7 September, which subsequently rose to 7.5 MPa, about 1.3 times the standard level. This combination of stress anomalies and the silent period in microseismic activity signaled the impending high-energy mining-induced earthquake event on 10 September. Source Mechanism and Microseismic Localization: Given that the 3308 working face advanced only 0.8 m by 10 September, with a limited goal area and no large-scale suspended roof, it is unlikely that roof fracturing alone could generate such a high-energy event. Microseismic localization shows that the event did not occur within the working face or its roof and floor but rather in the roof of the fault-protected coal pillar behind the 3308 face, near the DF60 fault. This suggests that the disturbance from mining at the 3308 face impacted the incompletely caved roof of the 3306 goat, the DF60 fault, and the DF60-protected coal pillar of the 3306 face, leading to roof instability, fracturing, and fault slippage. Source mechanism analysis indicates this was a mixed-type fracture (primarily shear), consistent with high-angle roof fractures and fault slippage. In summary, the 10 September mining-induced earthquake event was primarily triggered by mining disturbances during the initial extraction at the 3308 face, causing sudden roof collapse in the shallow goal of the 3306 face and the DF60-protected coal pillar, potentially accompanied by DF60 fault slippage. The sensation of vibration and sudden strong airflow reported by underground personnel further supports this conclusion. Although this mining-induced earthquake event did not cause casualties or equipment damage, it disturbed the stress balance near the cutout of the 3308 face, intensifying the stress concentration effect in that area. (2) For the high-energy mining-induced earthquake event on 10 September:  
Stress Analysis: Prior to the 20 December event, stress levels on both roadways at the 3308 working face increased, followed by a decrease after the event. This aligns with the typical pattern of mine mining-induced earthquake events within the working face and its roof and floor, where stress concentration and elastic energy buildup within the coal and rock mass are relieved after the release of accumulated energy, resulting in a decrease in stress on both roadways. Microseismic Statistical Analysis: On December 15, the energy of microseismic events significantly increased, accompanied by an increase in daily advance from 0.3 m to 0.8 m. Subsequently, microseismic activity entered a \"silent period\", followed by the high-energy event on 20 December. Microseismic localization shows that this event occurred approximately 20 m above the track roadway of the 3308 working face. Source Mechanism and Microseismic Localization: The 20 December event was characterized by tensile fracturing, with energy and magnitude consistent with microseismic events induced by roof fractures.