A Fast Evaluation of the Seismic Moment Tensor for Induced Seismicity

An original method is proposed for the evaluation of moment tensor components using time-domain calculations of low-frequency displacement amplitudes with the first-wave polarities attached. The technique is suitable for applications involving large amounts of data that require a fast response time, such as those encountered in the analysis of induced seismicity. Simulation tests indicate an excellent agreement with inversions based on the far more labor intense spectral processing. The overall results of waveform simulation analysis allow the conclusion that this inversion approach is reliable in retrieving the geometrical aspects of the seismic source. Inversions for the pure-shear mechanism and a general mechanism, including a tensile component, are shown to be robust for various wave-type solutions, under reduced array coverage, hypocentral mislocation, and the addition of Gaussian normally distributed noise. The influence of errors in first-arrival polarities and low-frequency displacement amplitudes are subsequently studied for a better understanding of the applicability limits

Time-dependent seismic hazard in Bobrek coal mine, Poland, assuming different magnitude distribution estimations

The purpose of this study is to evaluate seismic hazard parameters in connection with the evolution of mining operations and seismic activity. The time-dependent hazard parameters to be estimated are activity rate, Gutenberg–Richter b-value, mean return period and exceedance probability of a prescribed magnitude for selected time windows related with the advance of the mining front. Four magnitude distribution estimation methods are applied and the results obtained from each one are compared with each other. Those approaches are maximum likelihood using the unbounded and upper bounded Gutenberg–Richter law and the non-parametric unbounded and non-parametric upper-bounded kernel estimation of magnitude distribution. The method is applied for seismicity occurred in the longwall mining of panel 3 in coal seam 503 in Bobrek colliery in Upper Silesia Coal Basin, Poland, during 2009–2010. Applications are performed in the recently established Web-Platform for Anthropogenic Seismicity Research, available at https://tcs.ah-epos.eu/

Assessment of failure mechanisms in deep longwall faces based on mining-induced seismicity

Failure mechanisms of the rock mass in the regions of maximum stress concentrations around a longwall face were assessed. In this respect, seismic events that result from changes in the stress field were analyzed to gain more knowledge about rock failure mechanisms in the proximity of the face area. A deep longwall mine developed at depths of about 3–3.5 km in South Africa was selected as a case study. Seismic moment tensor solutions were obtained for 32 seismic events with moment magnitudes in the range of 0.49 and 2.10. Through moment tensor decomposition, the dominant failure mechanisms were investigated by drawing focal mechanism plots. Further analysis was implemented by depicting the corresponding 3D radiation patterns of P-wave particle motions. Although the results cover various failure mechanisms, the dominant mechanisms are shear, implosional, and compressional failures. According to the results, most of the maximum principal stresses in the mine are compressive and oriented nearly vertical, which are in accordance with the gravitational collapses of the mined out areas. The results obtained from this research show that measuring and analyzing mining-induced seismicity can be a reliable measure to characterize the dominant failure mechanisms in a nondestructive manner and to provide a useful assessment of the stability of the longwall face in advance of extraction