Investigation on acoustic emission characteristics of fault stick-slip under different lateral pressures

Abstract

To explore the effect of different stress environments on fault-slip rockburst. The bidirectional shear friction experiments with different lateral pressures were conducted on pre-cracked syenogranites buried at 800m. The macroscopic statistical parameters (cumulative AE events, magnitude and b value) and local characteristic parameters (amplitude and dominant frequency) of acoustic emission during the stick-slip process under different lateral pressures were investigated. Besides, based on the fractal theory, the nonlinear characteristics of AE wave and its spectrum were analyzed. On this basis, the microscopic mechanism of fault stick-slip was discussed. The results show that the lateral pressure influences the friction strength of the fault and stick-slip characteristics. With the increase of lateral pressure, the proportion of transgranular shear fracture is increased, which leads to the increase of cumulative AE events and magnitude. The periodic decrease of b value is more significant at high lateral pressure. There is a good correlation between the high-magnitude AE event and the stress drop. The box-counting fractal dimension of AE waveform can reflect the difference of energy released during fault stick-slip. The AE frequency with phased response characteristics can effectively identify the evolution of the fault stick-slip instability at the laboratory scale. The sharp increase in the amplitude of dominant frequency can be regarded as one of the precursory features of fault stick-slip instability. AE frequency spectra have multifractal characteristics, which are different in different stages. The maximum multifractal dimension and spectral width can reflect the fracture scale of asperities.