侧向应力扰动对断层摩擦影响的实验研究

EFFECT OF LATERAL STRESS PERTURBATION ON FRICTIONAL BEHAVIOR: AN EXPERIMENTAL STUDY

利用双向伺服控制装置,对含有与最大主压应力σ1呈45°夹角的预切面的花岗闪长岩标本进行了摩擦实验,结果表明,在σ1方向位移速率恒定、侧向应力σ2恒定的条件下,粘滑间隔随滑动面上正应力的增加而增加,粘滑应力降也随滑动面上正应力的增加而呈线性增加。但当σ2叠加了高频小振幅的正弦波扰动时,这种相关性发生了明显的变化,应力降大小和粘滑间隔的离散度均显著提高,特别是应力降可能会大幅度增加。与σ1扰动的实验结果相比,σ2扰动对断层粘滑的影响更为显著,这主要归因于正应力变化使滑动面的非均匀性加剧。

The crustal movement shows obviously non-linear characteristics in time and space, and the tectonic deformation and related phenomena are undoubtedly affected by such non-linear mechanical process. Experimental study on frictional behavior under non-linear loading is helpful for understanding the effect of stress change on earthquake mechanism. In this paper, the frictional experiments on medium-scale granodiorite samples containing 45 ° precut surface have been conducted by using a servo-controlled biaxial rig, and the effect of lateral stress （ σ2 ） on friction has been studied. The experimental results indicate that the interval and stress drop of stick-slip events increase with increasing normal stress on sliding surface under constant loading velocity in the direction of maximum compression stress σ1 and constant lateral stress σ2- However, the relation is greatly changed when stress perturbation of sine wave with high frequency and small amplitude is added to σ2. Stress drop and interval of stick- slip events are obviously scattered. In particular, the magnitude of stress drop may tremendously increase. Strain measurement indicates that the perturbation of lateral stress increases the heterogeneity of strain distribution and release along fault, and stick-slip events with large stress drop and that with small stress drop are corresponding to strain release along whole fault and that along parts of fault, respectively. Compared to the previous experiment result of stress perturbation in σ1, the effect of perturbation in σ2 on stick-sllp is more obvious, meaning that change in normal stress may affect fault instability more greatly than change in shear stress, The experimental results imply that not only the effect of change in coseismic Coulomb stress on seismicity should be analyzed, but more attention should be paid to the possible effect of change in normal stress on fault when the fault interaction is considered.