Summary. 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

Seismic energy propagation from the hypocentre of mining-induced tremors usually causes an uneven distribution of the peak ground velocity PGV_Hmax in tectonically complicated structures, and consequently, an uneven distribution of damage to buildings located on the ground surface. This study aimed to estimate the impact of high-energy mining-induced tremors in fault zones on damage to buildings. In the study, we describe a case of one of the highest-energy mining-induced tremors E = 4.0 · 10⁸ J (local magnitude ML = 3.6) that occurred in the Upper Silesian Coal Basin (USCB), Poland. The hypocentre of the tremor was most probably located in the Barbara fault zone, one of the larger faults in that western part of the USCB. Numerous damaged buildings on the terrain surface were registered, both in the epicentral zone and at a greater distance from the epicentre, mostly from the southern side of the Barbara fault zone. We calculated that the tremor was characterised by a normal slip mechanism associated with the same kind of fault as the Barbara fault. The azimuth of the nodal planes was similar to the west-east direction, which is consistent with the azimuth of the Barbara fault. From the focal mechanism, the greatest propagation of seismic energy occurred in south and west-east directions from the tremor hypocentre towards the surface. It was found that from the northern side of the hanging wall of the Barbara fault, there were 14 instances of damage (19%), and in the southern part of a hanging wall, there were 58 (81%). Therefore, the directionality of seismic energy propagation is aligned with the focal mechanism acting in the Barbara fault. It has also been concluded that a width of the zone of up to about 1200 m along the Barbara fault is the most threatening on the basis of registered building damage in the geological conditions of USCB. The study has shown that in assessing the impact of mining-induced tremors on buildings and the environment, the disturbance of seismic energy propagation by larger faults should be considered.

The aim of the research was to determine the cause of high-energy rock mass tremors (energy E ≥ 105 J) in the area of longwall H-2a located in seam 409/3 in Borynia-Zofiówka-Jastrzębie colliery, basing on the analysis of geological and mining conditions, seismic activity, focal mechanism and local stress field. The research employed the method of seismic moment tensor inversion which provides parameters of focal mechanism (percentage share of its components: isotropic, uniaxial compression or tension, shear component; trend and dip of nodal planes, directions of tension axes and compression stress). The parameters describe processes occurring in focuses of tremors and they are clearly linked with stress conditions in a given area. The conducted tests showed that the cause of occurrence of high-energy tremors and three rockbursts in lot H while mining seam 409/3 with longwall H-2a, was dynamic destruction of roof rocks which could displace towards the cavity created after mining the seam. An additional factor significantly magnifying the process was the share of stresses, which originate from the faults in the area, existing in the rock mass. Results of the research provided additional information to determine the degree of rockburst hazard in the area. Because of very dangerous work conditions (stress parameters reflect the rock mass of high shear strength, where dynamic influence of tremors is stronger) mining activity in longwall H-2a was terminated a few dozen metres earlier than it had been originally planned

Exploitation in a coal mine “Bobrek-Centrum” of the longwall 6 in seam 510 has led to the occurrence of very high seismic activity. From January 2011 to June 2012 took place almost 3500 tremors with the energy of 102-104 J and 95 tremors of energy more than to 105 J. In an attempt to identify the character of that seismicity, calculations of focal mechanism parameters were carried out, and according to them local stress field was determined. Three periods of exploitation of longwall 6 were distinguished which vary in type of focal mechanism. Tremors, which occurred in exploitation periods I and III were characterized by normal slip mechanism, occurred due to domination of vertical principal stresses σ1, horizontal intermediate stresses σ2 and minimal ones σ3. Such stress arrangement characterizes local state of rock mass behaviour as a result of cracking and collapse of sandstone, tremor-generating strata during advancing exploitation. In exploitation period II, of non-shearing mechanism of foci occurred. That was the period of change of longwall run from the NE-SW direction to E-W direction, that is the period of so called “slanting” of exploitation front. It can be presumed that this type of tremor mechanism could have occurred due to a sudden coal bed load by superimposed roof strata, which may have led to extreme load conditions and to a dynamic disintegration of seam part. It was confirmed by geomechanical calculations, which indicated that in the region of rockburst existence on 19.07.2011, layers which were located above and under seam 510 in area of longwall no. 6 were strongly deformed locally causing compression of certain parts of seam.

The paper presents the characteristics of seismic tremors and rockbursts that occurred between 2001 and 2015. The characteristics are based on a general description of the geological structure of the Upper Silesian Coal Basin (USCB). The level of seismic activity in the analysed period changed a number of times and depended on the intensity of mining works and diverse mining and geological conditions in each of the five regions where tremors occurred (Bytom Trough, Main Saddle, Main Trough, Kazimierz Trough, and Jejkowice and Chwałowice Troughs) and which belong to various structural units of the Upper Silesia. It was found out that in the case of rockbursts the phenomena were recorded in three regions. These are: Main Saddle, Bytom Trough, and Jejkowice and Chwałowice Troughs. The so called Regional Rockburst Indicator (RWT) was estimated for each of the regions where the rockbursts had been recorded. The obtained values of RWT are presented against the Probability of RockBurst (PT) in a given area.