## 2 Materials and Methods
### Characteristics of the Database
#### 2.1.1 GEO Index  
The potential rock burst hazard is determined while planning new openings, which can be paralleled to a long-term rock burst prediction. First, the mechanical properties of coal and/or surrounding rocks (e.g., the uniaxial compressive strength), are considered. Moreover, places where the risk of rock burst is greater due to the properties of coal or surrounding rocks or the presence of factors affecting the stress level in the rock mass (e.g., edges of adjacent coal seams) are identified. Assessing the geomechanical properties of the excavated rocks is one of the basic methods of assessing the potential rock burst hazards. Numerous studies in this area have been carried out for many years in the mines of the USCB [46; 47; 48; 49; 50; 51]. However, most of the indicators for assessing the rock burst proneness in coal mines refer mainly to different coal types and rocks surrounding the coal seams. Only a few of them are used to assess the rock mass proneness, with careful consideration of its geological features. Until the 1970s, the natural proneness to rock bursts was assessed in the USCB only in terms of quality [46]. Then, indicators of rock burst proneness were developed based on the pre-failure stress-strain characteristics obtained during the compression of the sample. The first studies concerned the strain energy storage index \(W_{ET}\)[47]. This index was intended for coal. The coal sample is loaded to 81-90% of the breaking stress, unloaded to a value of about 5%, and repeatedly loaded until the sample is destroyed [46]. The \(W_{ET}\) index is the dimensionless ratio of the elastic deformation energy to the irreversibly lost energy during the sample deformation. For the conditions occurring in coal mines in the USCB, an attempt was made to collectively analyze the factors determining the rock mass proneness to rock bursts and develop an appropriate assessment scale. A geological and geomechanical system for assessing rock mass proneness to rock bursts, GEO, has been developed [46]. This system combines many elements that comprise the rock mass structure and properties in the Upper Silesian Coal Basin. For mines in the USCB, a GEO system was proposed to assess the proneness of the entire seam-surrounding rock system to rock burst [46]. All information on geological conditions in the vicinity of selected points in openings has been involved in the GEO index (e.g., depth, coal seam thickness, and distance of the coal seam from the thick layer of sandstone) [46]. This index also involves information about the geomechanical properties of rock mass and the maximum energy of tremors that may occur with a given rock mass structure. In addition, the GEO index contains information about the rock burst proneness of the entire seam-surrounding rock system. It includes \(W_{ET}\) index, rock mass number \(L_{g}\)[48], and rock mass bursting proneness index \(W_{TG}\)[49]. For each parameter, classes are specified that correspond to the points of the GEO system. Finally, the points associated with each parameter are summed up to give a GEO index value. The minimum, maximum, and average values of the GEO index in the database equaled 44, 134, and 101, respectively. The maximum number of points allowed in the GEO system (i.e., 134) was reached in about 2% of the samples. According to the scale for assessing the natural proneness of a rock mass to rock bursts in the GEO system, for approx. 3.7% of the samples, the rock mass was not prone to rock bursts (GEO index below 68); for approx. 30.8% of the samples, the rock mass was slightly prone to rock burst (GEO index between 68 and 90); and for approx. 65.5% of the samples, the rock mass was strongly prone to rock bursts (GEO index higher than 90). The distribution of the GEO index values, with division into rock bursts (1) and cases without damage and destruction in the openings (0), is shown in Figure 1a. Considering only rock bursts in the dataset, the calculated GEO index ranged from 75 to 134 (mean 109).