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Rock and Soil Mechanics

Abstract

Accurate acquisition of arrival time of microseismic signals is an important prerequisite for focal location, and the accurate acquisition of arrival time of P-wave and S-wave of microseismic signals has important theoretical significance. Based on the principles of time-frequency analysis and the arrival-time picking, the time-frequency analysis-downhill comparison method is proposed. According to the time-frequency analysis principle of this method, the position and rule of background noise, the frequency, amplitude and energy of microseismic signals before and after the initial arrival of P-wave and S-wave and smooth waveforms that facilitate the comparison of iterative averages can be obtained through spectrogram, power density spectrum and two successive FIR band-pass filters. By setting the mathematical expectation of the full wavelet amplitude as the threshold and iteratively comparing wavelet amplitudes of microseismic signals based on three relationships of power, arrival order and waveform overlap of P-wave and S-wave, the precise arrival time of P-wave and the arrival time of S-wave peak value are obtained. The advantages of this method over the improved STA/LTA method are compared by model tests and have been verified in an engineering example. The results show that: compared with the improved STA/LTA method, this proposed method can simultaneously pick up the precise arrival time of P-wave and the arrival time of S-wave peak value, while the latter can only pick up the accurate arrival time of P-wave. The average time difference and standard deviation of the former are 6.18 ‰ and 3.98 ‰ of the latter, respectively. Additionally, the average calculation time and standard deviation of the former are 43.99% and 10.54% of the latter, respectively. The failure ratio of the former is 0 while that of the latter is 15.63%.

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