Hi Don,

unfortunately, I must say, that in the multilayer conditions as in Ostrava-Karvina Coal Basin, I did not see the nucleation phase of the main shock. Such big events are localised into the coal roof and their foreshock activity is low - some tens of events per day. The seismic activity from the coal seam is in the same time hundered times bigger - thousands events per day. On the other hand, I saw the increasing of seismic activity from the coal roof before the main shock. But it was not the nucleation phase which is some hours long before the event with energy about 1E5 - 6 J (i.e. m=2).

My apparatus is data acquisition system based on PC with 12-bit A/D converter, good amplifier and intrinsically safe barrier. Timing is by the radio from Germany. Records are triggered by amplitude of event with pretrigger. ON OKCB is in operation about 9 apparatus for seismoacoustic that can simultaneously monitor 18 longwalls and 6 apparatus for seismology that monitor the whole area of OKCB. The low treshold (sensitivity) of SA apparatus is about 1 J (m=-2) from the area 300 x 300 m. The precision of localisation is about 20 m. For SL apparatus is about 20 J from the whole OKCB which is about 12 x 8 km x 1 km.
Pavel