Focal Mechanism of Strong Ground Seismicity Induced by Deep Coal Mining.

In recent years, strong seisms are triggered frequently during deep coal mining process, which seriously threatens the safety of underground miners and ground residents, as well as restricts the productivity and effectiveness of mining activities. It is essential to investigate focal mechanisms and source parameters of seisms for understanding the rock fracturing, the rupture scale and the failure mode. However, the focal mechanism and the internal relationship among source parameters lack systematic research in deep mines. More than 11473 seismic events have been recorded so far in the No.6 mining area of Dongtan Coal Mine, among which 27 events with moment magnitude MW ≥ 1.0 occur in panel 06/63. Results show that Savage model (ω3) has well applicability for spectral analysis in 27 observed seismic events and accords with the characteristics of fast attenuation of displacement amplitude in high frequency. Focal mechanisms of seism events are mainly dominated by pure shear failure and mixed shear failure. Based on the moment tensor inversion (MTI) method and genetic algorithm (GA, a deep learning method), the correlation of source parameters is revealed, and the scale and occurrence of source rupture are calculated effectively. The new preliminary criterion for determining rock fracture type by the dip angle δ and inclination angle θ of fracture surfaces is proposed. Formation mechanisms of strong seisms can be categorized into two types by using the spatial distribution characteristics of fracture surfaces and P–T projection. Meanwhile, we believe that the two mechanisms cross and promote each other under mining disturbance and overburden loads. Highlights: The moment tensor inversion (MTI) method is used to distinguish the focal mechanism of mine seisms. The correlation of source parameters is developed based on Fourier transform (FFT) method and Savage model. A new preliminary criterion is proposed by the dip angle δ and inclination angle θ of fracture surfaces to determine the fracture types of the rock mass. Formation mechanisms of strong seisms are discussed in detail by using the P–T projection and the fracture surface occurrence. [ABSTRACT FROM AUTHOR]