Study on the characteristics of AE and charge induction signal during different dip angles fault stick-slip process with fault slip rockburst

Fault stick slip instability can easily induce fault slip rockburst. In order to further explore the stick-slip evolution characteristics of faults with different dip angles and AE and charge induction multi-source precursors，bidirectional friction tests were carried out on syenitegranite with faults with different prefabricated dip angles. The accumulated energy and spectral characteristics of acoustic emission and charge induction signals during fault stick-slip were analyzed，the AE sources were located，and the nonlinear characteristics of AE and charge induction time series were studied based on multifractal theory. Three quantitative indexes(maximum multi-fractal dimension <italic>D</italic>_{<italic>q</italic>max}，spectral width Δ<italic>α</italic> and multi-fractal parameter Δ<italic>f</italic>(<italic>α</italic>)) with good correlation with stick slip instability were constructed，and the following conclusions were drawn：(1) With the increase of fault dip angle，the fault failure mode changes from sliding failure along the plane to sliding failure through the plane，which increases the intensity and energy of AE and charge induction signals. (2) The maximum multi-fractal dimension <italic>D</italic>_{<italic>q</italic>max} and spectral width Δ<italic>α</italic> of the AE and charge induction signals gradually increase with the increase of fault dip angle. The maximum multifractal dimension and spectral width of the AE and charge induction signals can reflect the difference of energy released when the fault stick slip instability or severely damaged. The multi-fractal parameters Δ<italic>f</italic>(<italic>α</italic>) of AE and charge induction signals are all less than 0 when the fault is instability or severely damaged.，and the critical value of Δ<italic>f</italic>(<italic>α</italic>) can be used as the prediction index of fault stick slip instability and severe failure. (3) Compared with the AE and charge induction signals generated by shear slip failure along the plane of 34°and 45°faults，the AE and charge induction signals generated by 56°faults through the plane slide failure has lower dominant frequencies. It can be considered that the dominant frequencies of the AE and charge induction signals are related to fracture scale.