Characteristics of seismic activity of the Upper Silesian Coal Basin in Poland

The Upper Silesian Coal Basin (USCB) in Poland is one of the most seismically active mining areas in the world. Seismic observations supported by the Central Mining Institute date back to the 1950s, and include an extensive mine tremors data bank, which has been in operation since that time. More than 55 900 mine tremors of energy E 10 5 J (local magnitude M L 1.5) occurred over the period 1974-2005. In the USCB, two types of tremors can be distinguished. These are the so-called 'miningtectonic' seismicity and 'mining' seismicity. The 'mining-tectonic' seismicity results from the interaction between mining and tectonic factors. These seismic events appear to be located in tectonically disturbed zones and their sources are visibly more energetic. The mine tremor source mechanism can mostly be the normal dip-slip fault with a marked strike-slip component in the source region. The rupture plane azimuths and dips of these seismic events correlate well with the strike and dip of the pre-existing local faults, in the vicinity of which the mine tremor sources have been located. The generalized mine tremor source mechanism of the events under consideration contributed a less than 15 per cent implosion component, an about 15 per cent uniaxial compressional component, and an about 70 per cent shear component to the total seismic moment tensor solution.