Induced seismoacoustic events in burst-prone areas of West German coal mines

In underground coal mines of the Ruhr district test drillings are applied to obtain information about the actual stress-situation of burst-prone areas. Drill cuttings per metre and also audible cracking noises are the main criteria for such test drillings. Measurements of seismic seam-reactions and of technical drilling-parameters (rotational speed, torque, axial drilling force) during test drillings might give additional criteria for improved interpretations of test drillings (and also destressing drillings). With a newly developed portable, intrinsically safe measuring device it is possible to register and pre-evaluate signals of seismic seam-reactions and of drilling parameters. Signal analyses of seismic events and technical drilling parameters are shown together with some first results. Ahead of long wall faces high stresses are induced, which trigger a lot of seismoacoustic events. In a retreat mining area with a size of about 210 m X 900 m within ten months seismic signals of more than 36000 events were recorded with an especially designed, intrinsically safe equipment. With frequency- and dispersion-analyses it is shown that mainly Love- and Rayleigh-seam-waves contribute to the signals. Sophisticated computer programs allowed to localize about 87% of the events. The event-distribution is discussed with respect to the recognition of areas with high stresses.