Characteristics of coal mining microseismic and blasting signals at Qianqiu coal mine

Abstract

The signal waveforms caused by blasting events, which are similar to the microseismic (MS) signal waveforms caused by mining activities, are very common during the MS monitoring at coal mines. However, these blasting signals are not useful for monitoring and early warning of the coal or rock dynamic disasters by MS monitoring technique. To distinguish between the coal mining MS signals and the blasting signals, we studied the differences between these waveforms by analyzing the dominant frequency, signal duration, following peak attenuation, and multifractal parameters [Δα and Δf(α)]. The main results are: The coal mining MS signals have lower dominant frequency (below 80 Hz) and longer vibration duration (more than 2 s) than the blasting signals (dominant frequency above 80 Hz and duration less than 2 s). The following peak envelope curves of the two types of signals fit a power function. Moreover, the power exponent and fitting accuracy were obtained to describe the attenuated speed and stabilities of the MS signals. The coal mining MS signals attenuate slower, and the coda waves are more complex than the blasting signals. The dividing line of the power exponent between the mining MS and the blasting signals is 8. According to the multifractal theory, the mining MS signals have smaller spectral width Δα (below 1.2) and Δf(α) (below 0.3) than the blasting signals (Δα above 1.2 and Δf(α) above 0.3). The research results lay a foundation for the automatic identification of mining MS signals and blasting signals recorded in coal mines.