| Abstrakt: |
Abstract: Focal mechanisms of 400 mining induced seismic events were determined using seismic moment tensor inversion method. The seismic moment tensors were calculated in time domain for P-wave first arrivals. All the seismic events were induced in the vicinity of one longwall opening localised in the Halemba coal mine area (Upper Silesian Coal Basin, Poland). Assuming that the tremors occurring in the same area in short time intervals are generated by similar stress conditions, mean local stress tensors for sets of seismic events were calculated. Only shearing focal mechanism seismic events were taken into account. The stress tensors were calculated for ten succeeding seismic events. The study showed that the state of stress was very unstable in the investigated area. Variation of the local stress field manifested itself by instantaneous interchanging of the positions of main stress axes. Variations of the state of stress were probably the result of mutual interaction of lithostatic, mining and tectonic stresses. |
