Tectonophysical approach to the description of mining induced seismicity in the Upper Silesia

Abstract

Seismicity occurring in the Upper Silesian Coal Basin (the USCB) Is induced by deep underground coal mining and is relatively well recorded and recognized. The majority of tremors occurring there, is closely related to mining so only mining induced stresses were considered to be the cause of the tremors. The frequency energy distribution of mine tremors in the USCB has indicated the evident bimodal features: the lower energy mode, closely related to mining and the largest energy indicating the relation to the geological structures of the USCB. Therefore the research has been undertaken to explain if there is any tectonic influence on mine tremors occurrence and to formulate a seismotectonic model of state of deformation and stresses in the rock mass of the USCB responsible together with mining activity for the mine tremors generation. The obtained results indicate that tectonics plays a significant role in the occurrence of at least some of the largest mining tremors in the USCB area and the tectonophysical analysis can explain some relations in their occurrence. On the basis of seismotectonic model constructed for the USCB area we can conclude that the parameters of strain ellipsoid as well as of the seismic moment tensor and regional stress tensor for some mine tremors are almost the same. Some parts of the Upper Silesian Coal Basin (e.g. the zones of large latitudinal faults) are related to the large discontinuities in the deep crustal basement with active shear stresses. The equilibrium disturbance due to the reduction of vertical stress component caused by mining, erosion of the Carpathian overlap or the postglacial rebound may result in unstable behaviour in these zones and one can expect recent horizontal and vertical movements there. We also underline that the application of the optimum method of direct stress (strain) measurement it the rock mass for conditions of the USCB is necessary as well as that the modernization of seismological networks existing there is inevitable.