This paper describes the first experience in in situ determination of stress tensor changes during a longwall extraction. A device designed to measure deformations at the bottom of conical ended boreholes was used for the long term observation of stress changes induced by underground mining activity.
Classical Russian S-5-S pendulum seismometer was modified for recording of the rotational components of ground motion. This seismometer was used for monitoring of mining induced seismic events in the Karviná region (Czech Republic). Together, three translational components of ground vibration velocity and one rotational component of ground vibration velocity around the vertical axis were recorded. Elaborated mining induced seismic events with epicentral distances up to 9 km were recorded in Doubrava locality, where the exploitation of black coal is still active. Numerical study of measured component attributes of mining induced seismic events is presented in this paper, namely squared Morlet wavelet coefficients and squared coherence spectrum between rotational and translational components. Squared Morlet wavelet coefficients enable to analyse time-and-frequency structure of elaborated signal, e.g. dynamics of the onset, evolution and disappearance of typical periods of the harmonic peaks, etc. Spectral measure of coherence was applied here for investigation of synchronization effects in 2-dimensional time series of translational and rotational components.
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