In this paper, a rockburst is considered as a complex physical and rock mechanical process. The dynamic stress generated by the seismic load that is caused by a seismic event has to be added to the static stress in the rock mass in order to create this phenomenon. The seismic load near to underground workings is directly related to the source mechanism and radiation directivity of seismic tremors. The relation between the seismic load and the directivity of the seismic source radiation is presented and analysed using several cases of rockbursts in Polish coal and copper mines. The method, which utilizes directivity of seismicwaves resulting from different source mechanisms, contributes significantly to increase our knowledge of the rockburst phenomenon and provides an explanation of its origin.
Rockbursts belong to a group of natural hazards, the occurrence ofwhich has the characteristics of a mining disaster. Rock masses that are suddenly thrown into the mine workings cause a chain reaction of mechanical damage to the support and equipment and pose a threat to the crew; roof fall is also a frequent occurrence. As a result of rockbursts there is a loss of the functionality of workings, interruptions in production and various types of property damage and injuries to the mining crew (Dubi´nski & Konopko 2000). The proximate cause of the occurrence of a rockburst is always a seismic disturbance. It is connected with a dynamic release of seismic energy, typically of a high magnitude, which reaches the mine workings in the form of seismic waves, thus affecting their stability and causing rockbursts in the form of the above-mentioned effects.
The phenomenon of a rockburst occurs in many mining basins around the world, both in hard coal and metal ore mines. In Poland, the seismicity induced by mining activities and the accompanying rockbursts occur in the hard coal mines in the Upper Silesian Coal Basin (the USCB) and the copper ore mines in the Legnica-Glogów Copper Region (LGOM).