Moment Tensor Inversion and Coseismic Stress Characteristics of Mining-Induced Seismicity in Coal Pillar Area

Coal pillars are often set up to protect roadways from rockburst hazards in the working face; however, the presence of coal pillars is a “double-edged sword” because unreasonable settings can increase the risk of coal mining. In this study, we used the 73 upper 11 working face in the Baodian coal mine as the engineering background to explore the instability characteristics of coal–rock mass in coal pillar areas. The failure types and focal mechanisms of 21 events ( M L ≥ 1.2) in coal pillars were investigated using the moment tensor inversion method. Considering the limitation that moment tensor inversion assumes a point source, we inverted the stress field of the remnant coal pillar area on both sides of the working face to find the dominant controlling factor of seismicity. These inversion results were then used as input terms for a static Coulomb stress simulation to identify the characteristics of the coseismic stress caused by induced seismicity clusters and the influencing mechanism of subsequent seismic activities. Our results indicate that (1) the 21 high-energy (HE) seismic events were primarily compression failures, generally distributed on the floor, and the focal mechanisms of these events were primarily characterised by normal fault slips, whilst a few high-position events were reverse fault slips. Furthermore, (2) the stress field of the coal pillars differed from that of the in situ stress measurement; therefore, we inferred that these events were induced by mining, with their dominant control factor being the maximum compressive stress ( σ 1 ) extrusion with a high plunge. Lastly, (3) the locations of 37 microseismic (MS) events on August 1 and August 2, 2022 confirm that the mining-induced events triggered subsequent MS activities at a rate as high as 81%. Notably, 20 (54%) of these MS events were close to the isolines zero of the Coulomb stress changes.