Understanding Rockburst-Generating Behaviors and Associated Seismicity by Using a Spatial Calculation Methodology with an Energy Density Index

Rockbursts have become one of the most severe risks in underground coal mining. A proper understanding of the relationship between the spatial activities of mining-induced tremors and the occurrence of rockbursts can provide effective insight into the evaluation of rockburst hazard as well as revealing their causes. A methodology for spatially calculating the seismicity involving the use of an energy density index was developed to identify the evolution of mining-induced tremors over time. The results showed that numerous tremors occurred during the excavation and mining periods, and those tremors were distributed in a spatially complicated fashion, and it was difficult to identify their evolution trends over time and assess the rockburst hazard. However, energy density clouds had obvious distinguishable trends that presented nucleation characteristics and followed obvious extension around the nucleuses until strong tremors took place nearby. Velocity tomograms indicated that evolution of energy density clouds was the response to the rising stress concentration in some local areas before the rockburst. Then the rockburst-generating journey was inferred; that is, the jump of stress in local areas of coal-rock masses results in the clustering and nucleation of microfractures firstly, and then as the microfractures developed, macrofractures appeared, bringing strong tremors which triggered the rockburst.