断层黏滑失稳过程声-电信号响应特征研究

Acoustic emission and charge signal response characteristics in the process of fault stick-slip instability

为深入探索断层黏滑失稳的阶段特性以及声-电多源联合前兆特征,对含不同预制倾角断层的正长花岗岩开展了侧压分别为5、15、25MPa的双向剪切摩擦试验,观察和分析了断层黏滑失稳过程的力学行为以及声发射、电荷感应信号的时频响应特征。结果表明:(1)侧压和断层倾角改变了断层的黏滑特征,进而影响了感应电荷量和声发射事件震级。侧压越大,间黏滑和黏滑失稳阶段的电荷量占比以及电荷累积速度越大。相较于56º断层,45º断层黏滑失稳时基于振幅的统计指标b值更小,大尺度破裂占比更大。(2)声-电信号幅值的分形特征可以反映断层面黏滑错动释放能量的差异。声-电信号频域的阶段性响应特点可有效辨识实验室尺度下断层黏滑失稳的演化过程,可以将声-电信号主频幅值急剧提高作为断层黏滑失稳前兆特征之一。临近断层黏滑失稳时声发射和电荷感应参量(能量、分形维数、频谱幅值)均呈现明显的“突增”特性。(3)声-电信号能量突增与黏滑应力降之间具有较好的对应性,但并不完全同步。断层黏滑失稳时,声发射会先于电荷感应产生高幅值信号。仅采用单一声发射或电荷感应信号来预警有可能造成信息漏报、误报,需结合声发射和电荷感应信号特征以实现声-电二元信号的相互补充与验证。

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.