Characteristics of Mining Tremors within the Near-wave Field Zone

Mining in the Upper Silesian Coal Basin, Poland, induces tremors, with magnitudes ranging up to 4.3. The recordings of mining tremors from the near-wave field and the far-wave field show different characteristics of ground motion.Knowledge of these characteristics, has an enormous practical importance when solving the problems of resistance of underground workings against seismic impacts. The near-wave field is characterized by a domination of the high frequency components of motion, and the seismograms often are a single pulse. Geomechanical interpretation of them leads to the conclusion that this pulse corresponds to a single exciting force. This fact is also reflected in the rockbursts: the potentially damaging ground motion which is restricted to the seismic source region.The seismometric data have shown that the peak particle velocities from a hypocentral distance of 200-300m, resulted in more than 3 cm/s. The peak ground velocities appear to be dependent on stress drop Δσ, and peak particle velocities reaching 5 m/s may occur. The computational example proves that in a thick coal seam the pulse with the stress σ = 1.8 MPa from the tremor at the short source distance can generate the rockburst.