Localisation of microseismic events can lead to catastrophic failure and collapse of underground and surface openings. Given that the localisation does not happen simultaneously - the localisation zone is formed in a certain location and then propagates in a crack-like manner – the arrival times of the microseismic or acoustic pulses are synchronised. Thus the synchronisation can be used as an indicator of the localisation and the approaching failure. The proposed localisation indicator is based on computing the power spectrum of the sequences of arrival times, which is the Fourier transform corresponding to delays in the pulse arrivals. The actual indicator is the relative difference between the frequency dependence of the energy of the power spectrum of arrival times of the recorded and pure random sequences of arrival times. The highest values of the energy correspond to the 3D (cloud-like) localisation. The next highest values correspond to 2D (crack-like) localisation, which is considered to be a failure precursor.
Damage and strain localisations can lead to catastrophic failure and collapse of underground surface openings. While globally the strain localisation can be perceived as a result of bifurcation in the homogeneous solution of the equation of equilibrium (e.g., Rudnicki & Rice 1975), microscopically it is related to the localised accumula-tion of defects or microcracks whose position is dictated by the interaction with already created defects or other microstructural elements. The localisation can be detected by monitoring the microseismic events (or acoustic events in the lab), each event being produced by the generated defect. Experiments (e.g., Lockner, et al. 1991, 1992) show that the localisation does not happen instantaneously. Instead, it is synchronised such that the zone of acoustic events propagates stepwise in a crack-like manner. Currently the seismic/acoustic monitoring requires the use of complex systems capable of locating each event.
