Microseismic clustering degree: concept, algorithm and application of five-dimensional index of microseismic spatiotemporal evolution

Microseismic monitoring has become an important means of mine safety identification and early warning, but the spatiotemporal evolution mechanism based on microseismic and its correlation with rock activity still need to be solved urgently. At present, microseismic analysis mostly uses multiple indicators or comprehensive evaluation. However, the connection between different indicators is weak, resulting in a weak correlation or even contrary to the identification results. The massive microseismic events with different energy in the working face are all caused by rock fracture and rotary motion. Many small events are derived from the same source, so there is a certain correlation between microseismic events. Therefore, it is of great significance to study the microseismic spatiotemporal evolution of based on the microseismic index with rich connotations. Based on this, a microseismic spatial-temporal evolution index is proposed, which includes three dimensions of space, one dimension of energy and one dimension of time, a total of five dimensions: microseismic clustering degree. This index indicates that the rock stratum is often accompanied by large microseismic energy or spatial aggregation degree and time clustering when it breaks and rotates. The calculation formula of microseismic clustering degree under three factors including energy, space and time series is derived, and the generalization verification is carried out. Furthermore, the formula is used to calculate the microseismic clustering degree of microseismic events during the initial mine pressure and periodic mine pressure of the TingNan 307 working face, and the distribution law of the layer where the events with larger microseismic clustering degree are located is analyzed. The results show that the frequency of microseismic events in the immediate roof is larger, but the clustering degree of most events is not as large as that of the main roof. Events with high microseismic clustering degree can better reflect the variation law of mine pressure. Before and after the initial pressure and periodic pressure, the microseismic clustering degree of the main roof increased first and then decreased. This index breaks through the single analysis of energy frequency and spatial frequency, which can reduce the influence of microseismic in caving zone, and more intuitively reveal the overall law of mine pressure appearance. Microseismic clustering degree has the characteristics of one index containing multiple dimensions. It can not only be applied in mines, but also be extended to all geotechnical fields such as tunnels, hydropower stations, and metal mines, which have important field significance.