Analysis of Unusual Activity
Cases of anomalous seismic activity occur when, for instance, a specific area of the mine demonstrates a stronger response to production in comparison with its neighbours, or an unexpected activation (seismic swarm) is observed.
Analysis of these is based on careful reprocessing and inversion of mechanisms of a representative set of events in the area of interest. The aim is to get a mechanistic explanation of the phenomenon, e.g. whether the events are related to fracturing in a solid rock mass, or to slip on weaknesses (faults, joints), or to failure of components of the mining or regional support system (abutments, faces, pillars).
More in-depth analysis represents description of the anomalous activity in terms of a numerical stress-strain model. The benefit of such approach is in the ability to quantify efficiency of preventative measures (e.g. changing of the mining layout or sequence of mining). The numerical model is calibrated using seismic data. For instance spatial positions of seismic events and their mechanisms will be correlated with amplitudes and orientations of stresses derived from the model in the case of seismicity associated with co-seismic deformation of the solid part of the rock mass. For the case of pillar failures, the initial state of the model (failed/non-failed pillars, residual pillar strength) and pillar failure criteria will be constrained using seismic data.