TEMPORAL AND SYSTEM SPECTRAL ANALYSIS OF INFRASONIC SIGNALS IN THE ATMOSPHERE GENERATED DURING A MAN-MADE CATASTROPHE

The work objectives are to present the results of observations of waveforms and the system analysis of the infrasonic signals accompanying the multiple explosions that occurred during a great man-made catastrophe near the Town of Ichnia (Ukraine) on October 9-10, 2018. The depot (50 degrees 51'45 '' N, 32 degrees 23'39 '' E) occupying a 1.685-acre surface area contained 69,500 tons of ammunition. The observations were conducted using infrasound and earthquake monitoring equipment of the Main Center of the Special Monitoring of NCCTOSM, SSAU. The Malyn infrasound station is equipped with the microbarograph recording fluctuations in the 0.3-10 Hz range of frequencies. The technique of data processing in the present study was as follows. First, the temporal dependences of relative pressure in the infrasonic wave were converted into units of pressure. Further, these dependences were filtered by band-pass filtering in the 0.2 - 5 s period range. Then, the system spectral analysis of filtered dependences was applied using mutually complementary the short-time Fourier transform, the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods, and the wavelet transformation employing the Morlet wavelet as a basic function. The features of the waveforms, amplitudes, and spectral content of the infrasonic signals generated during the man-made catastrophe and propagated over long distances (218 km) from the ammunition depot near the Town of Ichnia (Chernihiv Province, Ukraine) on October 9-10, 2018 have been investigated. It was shown that an upward trend in the amplitude and the period of the predominant oscillation were observed when the energy release increased from 4.1 to 49.9 tons of TNT. The duration of the oscillation trains increased from 2.5 to 7 s. The analysis revealed that the harmonics in the 1-2 s period range were predominant when the energy release was equal to 49.9 tons of TNT. It was calculated that the average celerity of waves varied within 300-333 m/s. The main scatter diagrams are plotted.