Abstract
Underground mining of coal seams in the Upper Silesian Coal Basin in Poland is accompanied by seismic activity of varying magnitude. The investigations which have been performed for several years distinguished high energy mine tremors connected directly with mining or coupled with geological structures, such as large faults. In mined seams, local fault zones occur. Faults in these zones are usually small, with throws comparable with coal seams thicknesses. Local fault zone may be responsible for the occurrence of high energy tremors as well as large faults, as presented in this article. An analysis of source mechanism of high energy tremors generated during longwall mining of the coal seam No. 510, with presence of a local fault zone, in one of the Polish hard coal mines in the Upper Silesian Coal Basin was performed. For this purpose, the seismic moment tensor inversion method was used. In most of foci, the process of shear predominated. Determined nodal plane parameters were correlated with parameters of faults forming the local fault zone. High energy tremors were generated mostly by dislocations on faults of the local fault zone. Weakening of roof rocks in the neighborhood of local fault zone takes an important role too, and was responsible for share of implosion in the focal mechanism.
Highlights
Underground mining of coal seams in the Upper Silesian Coal Basin generates mine tremors, including those with high energy
Focal mechanism of mine tremors could be calculated with the use of seismic moment tensor inversion method
The only exception to this criterion is a focal mechanism type (RE) of tremor No 5 (Table 1), where the share of double couple of forces (DC) component equals almost 50%, the share of uniaxial compression is higher than 40%, and the implosion practically does not matter (Table 1)
Summary
Underground mining of coal seams in the Upper Silesian Coal Basin generates mine tremors, including those with high energy. The determination of mechanisms which are responsible for the occurrence of mine tremors is possible with the use of seismic moment tensor inversion method. The method of seismic moment tensor inversion was applied for determination of source mechanisms of high energy tremors induced during mining of coal seam No 510 in one of the coal mines in the Upper Silesian Coal Basin, in a certain time interval. The local fault zone was the main factor influencing the high energy tremor occurrence This knowledge was applied for determination of rockburst prevention methods in the longwall and will be useful for seismicity forecast during planning of further longwall mining
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