Dominant Directions of Epicenter Distribution of Regional Mining-induced Seismicity Series in Upper Silesian Coal Basin in Poland

The regional mining-induced seismicity of the Upper Silesian Coal Basin, Poland forms two major and two minor spatial clusters. The directional patterns of seismic series from the major clusters were studied with the use of the analysis of deflections. The seismic series is parameterized by the deflection angle of the straight line connecting epicenters of every two consecutive events, measured from NS direction. The trends of epicenter migration are characterized by modes of distribution of the deflection angle, estimated by the nonparametric kernel method. The distribution of deflection angles for the studied seismic series is not random. Altogether four trends of epicenter migration have been identified: two are connected with the subseries of events that belong to the same cluster and are related to the shape of the clusters, whereas the other two, linked to the subseries of events that alternate between the clusters, indicate that mutual positions of events in such series are not random. The results support recent hypotheses pertaining to low tectonic instability of this region.