Coal exploitation in the Upper Silesian Coal Basin is associated with rockburst hazard. This hazard is minimalized by active rockburst prevention, where torpedo blastings in roof-rocks take very important place. The estimation of the torpedo blasting effectiveness becomes significant under exploitation in difficult geological and mining conditions, where the high danger of rockburst occurs.

Pioneer investigations lead to estimate of the torpedo blastings effectiveness on the basis of an analysis of focal mechanisms of the induced mining tremors. The study has been carried out in the Bielszowice coal mine in cooperation with the Faculty of Earth Sciences of the University of Silesia. The torpedo blastingswere performed during exploitation of the seam 507 with the longwall 307b. Each blasting provoked a tremor immediately. The parameters of the focal mechanisms for each provoked event were estimated by the FOCI software.

Beside tremors foci with an explosive mechanism, related only to the detonation of an explosive, the occurrence of tremor foci with a shear mechanism has been confirmed. Shear mechanism in provoked tremors proves that blastings caused the motion of rock masses, what is connected with stress drop in the rock mass. The results have been associated with geological and mining conditions.

1 Introduction

Coal exploitation under condition of a rockburst hazard determines active rockburst prevention applying, where torpedo blastings occupy a prominent place.An estimation of the blasting efficiency becomes particularly important during the exploitation in difficult geological and mining conditions.

The focal mechanism studies with seismic moment tensor inversion method were performed for the tremors induced by torpedo blastings in the longwall 307b during exploitation of the seam 507 in the Bielszowice coal mine. Focal mechanisms were calculated by the seismic moment tensor inversion based on the analysis of seismic waves generated in the focus and registered by the appropriate number of seismometers surrounding the source.

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