Abstract
Physical processes occurring in the focus of tremor can be identified by solving a focal mechanism via the seismic moment tensor inversion method. In this article the estimation of focal mechanisms of strong mining tremors (according to Polish law tremors of energy higher or equal 1·105 J), which occurred during longwall mining of coal seam no. 507 in one of the hard coal mines in the Polish part of Upper Silesian Coal Basin was performed. Totally 7 strong mining tremors with the local magnitude from 1.84 to 2.52 were analysed. The most probable geomechanical processes in the foci of these tremors have been reconstructed. An attempt to determine the correlation between the edges of overlying seams no. 502, 504 or 506 and strong mining tremors occurrence has been made. The strike of determined nodal planes is in accordance with the azimuth of mentioned edges. The difference between them (absolute value) varies from 0.3° to 34.1° (on average approximately 19°).
Highlights
Rockburst hazard accompanies the underground extraction of coal seams in the Upper Silesian Coal Basin (USCB)
Because the norm L1 has lower dependence on possible large errors, caused e.g. by random noise produced by mining operation or transport machines, results obtained with it have been accepted as final (Table 1)
The most probable focal mechanisms of strong mining tremors, occurred during longwall mining of coal seam no. 507 in one of the hard coal mines in the USCB have been determined via the seismic moment tensor (SMT) inversion, and in all cases a shear mechanism was present
Summary
Rockburst hazard accompanies the underground extraction of coal seams in the Upper Silesian Coal Basin (USCB). The focal mechanism can be determined with the use of the seismic moment tensor inversion method This method enables estimation, what kind of processes were present in the focus of tremor (e.g. explosion or implosion, uniaxial compression or tension, shear). This can be further correlated with geological or mining factors. We have analysed the focal mechanism of 7 strong mining tremors (energy ≥ 1·105 J), which occurred during longwall mining of coal seam numbered 507 in one of the hard coal mines, located in the Polish part of Upper Silesia Coal Basin (USCB), on the main anticline. In the light of obtained results, an evaluation of rockburst prevention for selected longwall has been made
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