SPACE-TIME CORRELATIONS OF B-VALUES WITH STRESS RELEASE

A total of 1503 events for a 2-month period associated with a m(N) 2.6 rockburst is investigated for possible space-time correlations between low magnitude (-1.1 to -0.4) b values and several estimates of stress (static stress drop, apparent stress, and dynamic stress). Spatial variations of decreasing b values were found to be well correlated with increasing stress release estimates for time intervals prior to the rockburst and following the aftershock sequence. The strongest correlation to b value was with the dynamic stress drop, having correlation coefficients of 0.87 and 0.79 for the two intervals, respectively. The rockburst was found to actually occur at the intersection of the spatial coordinates corresponding to the largest gradient in b value. Based on these correlations, we conclude that the low magnitude seismicity is an indicator of the stress state within the rock mass, and can be used to study and forecast stress patterns in the vicinity of an impending major event. Time variations, however, did not show the same clear correlations and these are discussed in terms of departure from steady state conditions. Regardless, our results favour the use of b values in a spatial context rather than in a time analysis approach, and we consider that b values provide valuable information regarding the changing stress conditions within the seismogenic volume.