Spectra, energy, and fractal characteristics of blast waves

Using a portable microseismic monitoring instrument, we monitored blast waves at different distances from the blast center and analyzed their spectra, wavelet packet energies, and fractal characteristics. The results show that with increasing blast-center distance, the main frequency bands become narrow and the main frequency decay is governed by a power law (f. = 424.98 l(-0.72)). The energy of the wavelet packet is concentrated within the main frequency; energies associated with high frequency bands decay quickly, whereas for the low frequency bands (low to 78 Hz), the percentage of the total energy in these bands presents a rising trend of around 42% and 71% at blast-center distance 30 m and 110 m, respectively. In addition, the correlation dimension D of the blast wave tends to decrease with increasing blast-center distance; the correlation dimension D is 3.55 at distance 30 m and decreases to 1.26 at distance 110 m. The blast waves frequency spectra, wavelet packet energies, and fractal characteristics are inherent unity. These results provide an important basis for further study on the propagation law of blast waves in coal mines.