Materiały konferencyjne SEP 1992

Szkoła Eksploatacji Podziemnej * 92 463 usual (more thaji łOO events per hour) correlates well with the results of the test drillings (figurę 11: Thursday, Friday). The gap in figurę 11 on Thursday morning is due to a system failure Cinterruption of power supply). For further geophysical evaluations the seismic signals had to be anałysed in order to determine the kind of waves which contribute to the sełsmograjns. Coal i s a Iow ve 1 oc i ty 1 ayer embedded i n hi gh ve 1 oc i ty layers, such as shale or sandstone, and therefore an ideał seismic waveguide. Thus not only p- and s-waves will be registe- red but also surface waves "guided" within the seam, usually called "seam waves". Such waves are dispersive; group- and phase -velocities are freąuency depended. Figurę 12 shows a recorded section of typical seismograms of a seismoacoustic event. The seismograms have been plotted due to their source-distance and all tracks have the same over-all-sensłtivity. In this section some different parts of the waves are marked. The first onset with a velocity of 5.3 km/s refers to a p-wave, and the second with 2.9 km/s to a s-wave, both "guided" in the sandstone layer above of the coal seam. The third part of the wavetrain shows significantly higher signal-freąuencies, the velocity of 1.1 km/s approaches the s-wave-velocity within the coal. The biggest amplitudes near to the end of the signals refer to the "Airy-phase" with a velocity of 0.9 km/s. The beginning of the third part with higher signal freąuencies is relatively sharp (middle-tracks of figurę 12). This is due to the fact that all vełocities of the seam waves approach the vaiue of the s-wave- velocity of the coal with increasing signal-freąuency, so that a lot of energy is concentrated within a relatively narrow time- window. Other possibilities to characterize the seismoacoust ical s i gnałs are hodograjn-ca1culat i ons and frequency-analyses. An example is shown in figurę 13. The left side shows a typical seismoacoustic signal registered with a 3~component probe. The seismograms are rotated into a coordinate system depending on the direction to the source. The first tracę shows the particie ve1oc i ty parałlei to the ray {P-po1ar i sat i on, Ray1e i gh wave), the second tracę shows the particie vełoclty vertical to the ray