ABSTRACT
It is useful to monitor an attenuation field because changes in rock medium physical parameters exert a significant influence on it. However, the attenuation field can only occasionally be reconstructed because the attenuation effect is very sensitive to various disturbing factors. One of the most important is the lack of control of seismic energy emitted by sources. In the surveys, data are collected by a set of receivers placed on the edges of the investigation area. As sources of the seismic waves a series of controlled blasts detonated in various places is used. However, some errors occur because all the sources are not identical. It is therefore very fundamental and important to check the difference by the source. To see the difference two series of measurement were made using six receivers and eleven sources located in the same places with the same coverage of ray paths. As explosion sources the same amount of blasting material in boreholes were used. To avoid any temporal change in attenuation field two series of measurement were carried out within about 2 hours time without the longwall coalface advance rate. The differences in maximum amplitude of seismograms between two series were large, but were accounted for by variation in source energy. However, differences in an area-averaged attenuation were small. For both series an attenuation field was reconstructed based on the inversion of the maximum amplitudes reads with correction of geometrical spreading effects. Generally, differences in attenuation field are not greater than 20 % between two series for the most studied area with sufficient coverage of ray-paths.
