Fractal Study of Micro-seismic Energy of Fully Mechanized Caving Island Working Face

In order to study the laws of mining-induced micro-seismicity of island working face and prevent the coal rock dynamic disaster, the hypo-central location, energy, micro-seismic event and moment magnitude of micro-seismicity were investigated during the development of mine tremors by means of micro-seismic monitoring in the field and theoretical analysis, with the engineering background of N1202 island mining face of Yuwu Coal Mine. Based on fractal theory, an energy fractal analysis method of micro-seismic activity is proposed to reveal the variation of energy fractal dimension during the process of mine tremors and it is verified that the micro-seismic energy distribution caused by mining has fractal characteristics. The results show that during the whole monitoring period, the micro-seismic activity is dominated by medium and high energy release. The hypo-central location of mine tremors is in the roof, floor and coal seam of high stress concentration area of 30 m to 70 m in advance of working face, which is close to the haulage gate. The moment magnitude of mine tremors is 1.05 Mw and the energy release is more than 10⁸ J. In the period of “earthquake deficiency” before mine tremors, the cumulative energy, moment magnitude, number of events and fractal dimension of energy in a day are in a lower value. After the cumulative energy, moment magnitude and fractal dimension began to increase; the higher value would be reached on the day of mine tremors. The larger value of the fractal dimension, the higher proportion of the high energy release events.