Every year, a few rockbursts with fatalities and several hundred meters of damaged excavations have occurred in the mines of the Upper Silesia Coal Basin (USCB) in Poland. This paper presents a method for assessing the levels of seismic and rockburst hazards, using continuous seismological observation in the Bobrek coal mine. This assessment is based on the study of the Gutenberg-Richter (G-R) relation for current and past mining in the coal field. According to many laboratory and field studies, the b-value may be an indicator of fluctuations in stress levels (Scholz, 1968; Gibowicz, 1974; 1979), and the consequent seismic hazard. The novelty of the presented research is the development of a quantitative criterion based on b-value changes, calculated in moving time windows with a 1-day step, and the anomalies resulting from the comparisons of the temporal values of b with its average value for the past seismicity in the field of coal mining; A(G-R) =[(b(m) - b)/b(m)] .100% (where bm is the average value of b for the field of coal mining and b is the temporal value of coefficient b, calculated in time windows). This approach allows us to standardize the criterion to the current values of b in the investigated area (Table 1). In many measurement examples, high values of the temporal anomaly AG-R and at the same time downwardly trending and low b-values before the occurrence of strong mining seismic events were documented in this paper and in studies by Pierzyna (2014). Particularly interesting results were obtained from mining and geological conditions that led to the formation of local zones of stress concentration (Dubinski, 1989), and increases in seismic activity and seismic hazard. The b-value criterion is in agreement with the four basic levels of rockburst hazard used in Polish coal mines (Mutke et al., 2015).
