The Mean Local Stress Tensors for Halemba Coal Mine Area

摘要

Focal mechanism of 543 mine tremors occurred in 1995 in Halemba coal mine area (the Upper Silesian Coal Basin, Poland) were determined using the seismic moment tensor inversion method. The DC component was dominant in mechanisms of majority of tremors. On the basis of focal mechanisms solutions, mean local stress tensors in one-month time intervals were calculated applying direct inversion method developed by Angelier (1979). The research showed that the state of stress in the investigated area was very unstable. Fast and sweeping changes of main stress axes orientations were observed. The mining put the rock mass in the state of unstability. The state manifests itself by instantaneous interchangingof the positions of maximum and minimum axes.