正应力扰动对断层滑动失稳影响的实验研究

Effect of normal stress perturbation on frictional instability:An experimental study

利用双轴伺服控制加载装置,采用三块花岗闪长岩标本组成的含有两个滑动面的直剪结构,开展了摩擦滑动实验.实验中通过在垂直滑动面的载荷上叠加正弦波状和方波状的扰动,研究了正应力扰动对断层黏滑失稳的影响.研究表明,在恒定的正应力和位移速率下,标本表现为规则的黏滑,叠加正应力扰动后,随扰动振幅的增加黏滑发生时间与扰动的相关性增大,黏滑应力降和时间间隔的分布趋于离散.黏滑应力降和时间间隔的平均值随平均正应力的增加呈线性增长,扰动叠加后黏滑应力降的离散度随平均正应力的增加而增大;黏滑应力降和时间间隔主要受应力变化幅度的影响,而与应力变化的速率关系不大.剪应力和正应力扰动都会对断层黏滑失稳产生影响,而正应力扰动的影响更明显.这两种扰动对断层黏滑失稳影响的机制存在差异,剪应力扰动只是改变断层滑动的推动力,而正应力扰动则改变了断层面上凹凸体的接触状态.

We have performed a series of frictional experiments with direct shear configuration of three granite blocks by using a servo-controlled biaxial loading machine.In the experiments,a small-amplitude sine or square wave is modulated to normal loading in order to study the effects of normal stress perturbation on stick-slip instability.The results show that under the constant average normal stress and the constant loading point velocity in shear direction,the sample behaves as regular stick-slip.After the stress perturbation is modulated,the correlation between the timing of stick-slip events and the perturbation increases with increasing perturbation amplitude,and stress drop and interval time of stick-slip events tend to be discrete.The average values of stress drop and interval time of stick-slip events increase linearly with increasing average normal stress,and the dispersion of stress drop increases with growing average normal stress after the stress perturbation is modulated.Stress drop and interval time of stick-slip events are mainly affected by the amplitude of stress perturbation but less by the perturbation mode.Bothshear and normal stress perturbation can affect the stick-slip behavior,while the effect of normal stress perturbation is more obvious.The mechanisms of two kinds of perturbation affecting stickslip behavior are different.Shear stress perturbation can only change the driving stress along the fault,while the normal stress perturbation can change the contact state of asperities on the fault.