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ANALYSIS OF INFRASOUND SIGNALS FROM EKIBASTUZ MINING BLASTS AT KURCHATOV, KAZAKSTAN

Infrasound signals have been detected from large mining blasts in Kazakstan by the infrasound arrays at Kurchatov and Borovoye. For one month of data (March 1999) from the Kurchatov cross-array, we have recorded 163 events from the Ekibastuz mining region (∆= 245 km, B-Az: 296°) in seismic channels, of which 63 (~43%) were detected in infrasound channels. For the same period of data, we have detected 122 events from the Kuzbass region (∆= 740 km, B-Az: 58°) in seismic channels. Of these, 10 events have ground truth information. No corresponding infrasound detection is found. We also have detected four events in seismic channels at Kurchatov from a relatively less active mine in the Novotaubinka area (∆= 197 km, B-Az: 123°). Infrasound signals from the Ekibastuz mining area at the Kurchatov array show two arrivals separated by about 60 s, though these arrivals can range between 40 and 90 s. The second arrival is observed in about 65% of the events (41 out of 63 infrasonically detected events). A simple ray tracing scheme through a suitable atmospheric model suggests that the first arrival that has a travel time of about 750 s propagates through the troposphere and is followed 60 s later by a stratospheric arrival. Best beams have been calculated for infrasound signals recorded at Kurchatov from the Ekibastuz and Novotaubinka regions. For Ekibastuz events, although the average best-beam azimuth from first arrivals varies within 3° to 7° from the seismically predicted azimuth, the phase velocity emerges slightly slower (about 280 m/s) than typical sound velocity of 330 m/s. The phase velocity for the second arrival, when present, is slightly higher, around 300 m/s. For two months of data from Borovoye (December 1999 through January 2000), we have recorded 161 events from the Ekibastuz mining region (∆= 381 km, B-Az: 113°) in seismic channels. The corresponding infrasound detection is very low (only 4). Infrasound detection is relatively high from nearby mines located NW of the array (∆= 65 km, B-Az: 326°). From this period of data, we have recorded 36 events from the Kuzbass mining region (∆= 1123 km, B-Az: 77°) in seismic channels. All of them have ground truth information. We were not able to detect positively any infrasound signals from the Kuzbass region at Borovoye. The infrasound signals that were recorded at Borovoye from the mines northwest and southeast of the array show one simple pulse with about 2to 3-s duration. Best beams calculated from these infrasound signals show that predicted velocity is slightly slower than nominal sound speed, although predicted azimuth is similar to or slightly off from the seismically calculated azimuth. Best beam for signals from the Kuzbass region could not be resolved with confidence. 24th Seismic Research Review – Nuclear Explosion Monitoring: Innovation and Integration