Abstract: The research focused on exploring the characteristics of fault stick-slip instability and the combined multi-source precursor characteristics of acoustic emission (AE) and charge signals through bidirectional shear friction experiments on syenogranite with faults of different dip angles under lateral pressures of 5, 15, 25 MPa. The mechanical behavior of the fault and time-frequency characteristics of AE and charge induction signals were observed and analyzed. The key findings and observations are summarized as follows. (1) Lateral pressure and fault dip were found to change the stick-slip characteristics, affecting the induced charge and the magnitude of AE event. Increasing the lateral pressure led to gradual increase in the proportions of induced charge and charge accumulation rate in the meta-instability stage and stick-slip instability stage gradually increase. Compared with 56° fault, the amplitude based statistical index b-value of 45° fault was smaller, and the proportion of large-scale rupture was larger. (2) The fractal dimension of amplitude was observed to reflect differences in energy released by the fault. Phased response characteristics of the frequency characteristics of AE and charge induction signals were identified as effective means to discern the evolution process of fault stick-slip at the laboratory scale. A sharp increase in the main frequency amplitude was recognized as one of the precursor characteristics. The AE and charge induction parameters (energy, fractal dimension and spectral amplitude) in the stage from meta-instability to stick-slip instability showed distinct “sudden increase” characteristics. (3) There was a good correspondence between the energy of AE and charge induction signal and the stress drop, although not entirely synchronous. AE signal responded to stick-slip instability before charge induction. It was emphasized that combining AE and charge induction signal characteristics is essential for achieving mutual complementation and verification of the acoustic-charge binary signal.

Key words: oblique fault, stick-slip, acoustic emission, charge induction, time-frequency characteristics