Numerical investigation of dynamic disturbance process induced by a mining tremor based on time-dependent moment tensor

Abstract

Coal bursts, arising from abrupt dynamic disturbances from mining tremors, are among the most critical dynamic disasters in underground coal mines. Understanding the dynamic disturbance process of mining tremors is crucial for unravelling the mechanism behind coal bursts and identifying high-risk zones. However, previous studies have often utilized oversimplified source representations to model the dynamic disturbances induced by mining tremors. These approaches may overlook complex wavefields resulting from the focal mechanism, leading to distortion in the dynamic disturbance process. In this study, a time-dependent moment tensor obtained from full-waveform inversion was employed as a more accurate source representation of mining tremors to model its dynamic disturbance process. Full-waveform moment tensor inversion was achieved in the time domain by decomposing the source time function (STF) into a weighted sum of several basis functions. To illustrate this methodology, a mining tremor that triggered a coal burst at Huating Coal Mine was selected as a case study. Based on a multi-layered geological model, the time-dependent moment tensor of this event was inverted and interpreted, revealing that the high-magnitude mining tremor spanned a duration of hundreds of milliseconds, rather than occurring instantaneously. Subsequently, a three-dimensional multi-layered FLAC3D model was constructed to reproduce the dynamic disturbance process of the mining tremor based on its moment tensor. The FLAC3D modeling revealed complex wavefields and radiated patterns. Obvious shifts in the peak zone of peak particle velocity (PPV) and principal stress magnitude (PSM) relative to the source position were observed in the coal seam due to the influence of focal mechanism and medium structure. Results from monitoring points within the coal seam show that a dynamic disturbance process characterized by complex cyclic loading and unloading at an intermediate strain rate, accompanied by intricate paths of principal stress rotation (PSR). Numerous monitoring results indicated that the PPV and PSM exhibit a logarithmic linear attenuation pattern as the target-source distance increases, and the dynamic stress magnitude is approximately three times the product of PPV and medium wave impedance. This modelling approach can enhance our understanding of the principal stress variation induced by mining tremors in a complex mining environment with coupled static-dynamic loadings.