Fractal Characterization of Temporal and Spatial Evolution of Microseismic Events Before Rock Instability

Disaster warning is crucial for coal mine safety. However, capturing the precursor information of disaster occurrence remains a challenging task, especially the spatiotemporal fractal characteristics of microseismic events before large-scale fractures in rock masses and their indicative significance for disasters. In this study, we proposed a method for precursor identification and early warning indication of high-energy microseismic events by a combination of temporal and spatial fractal of low-energy events based on a set of 78 days of on-site microseismic monitoring data. The rationality of this method was validated by numerical simulation, which focuses on the fractal characteristics of rock fracture morphology under compression loading. The results show: (1) Before the occurrence of high-energy microseismic events, the fractal dimension of the microseismic events in the time series was relatively low, and the variance and autocorrelation coefficient of the time fractal dimension showed an increasing trend, exhibiting a typical slowing down phenomenon. (2) The spatial fractal dimension of the microseismic events rapidly decreased to 1.3–1.5 before the occurrence of high-energy events, with an average decrease of over 0.48. (3) Microseismic events are associated products of coal rock mass fracture processes, and their uniqueness in time series and spatiotemporal evolution characteristics have important indicative significance for the incubation and early warning of coal rock mass disasters.