Discrimination of different blasting and mine microseismic waveforms using FFT, SPWVD and multifractal method

Abstract

To distinguish various blasting and mine microseismic (MS) waveforms, the time–frequency characteristics and non-linear characteristics of mine MS waveforms caused by mining activities and different blasting waveforms (loosening blasting, pre-splitting blasting and deep-hole blasting) are analyzed using fast Fourier transform (FFT), smoothing pseudo-Winger-Ville distribution (SPWVD) and multifractal method. The results indicate that (1) Time–frequency spectrum of SPWVD can show the dynamic change of energy with time and instantaneous frequency. For mine MS waveforms, the energy and instantaneous frequency show a gradual attenuation trend with time. The larger the fracture strength of coal and rock caused by blasting, the higher the energy distributed in low frequency zone. (2) The dominant frequency obtained by FFT can divide the four types of waveforms into two types. The dominant frequency of loose blasting and deep-hole blasting waveforms are greater than 135 Hz, while that for pre-split blasting and mining MS waveforms are less than 135 Hz. (3) The loose blasting and deep-hole blasting waveforms can be distinguished by duration. The duration of loose blasting waveforms are less than 220 ms, while that for deep-hole blasting waveforms are greater than 220 ms. (4) Multifractal parameters (Δα and Δf(α)) can reflect the difference of local fluctuation intensities and heterogeneities of different waveforms and be affected by dominant frequency, duration and post-peak attenuation. The Δα and Δf(α) of pre-split blasting waveforms are less than 0.78 and − 0.2, respectively, while that for mine MS waveforms are opposite.