脆塑性转化带Carrara大理岩断层稳定性的实验研究

Experiments on fault stability of Carrara marble across the brittle-ductile transition

为探究脆塑性转化带断层的力学性质和滑动稳定性,本文采用干燥的Carrara大理岩预切断层(saw-cut)样品,在气体介质三轴高温岩石力学实验仪上开展了摩擦实验研究,实验温度70~400℃,围压30~100 MPa,位移速率在0.08μm·s^(-1), 0.4μm·s-1, 2μm·s^(-1)之间切换.实验力学数据揭示,不同围压下Carrara大理岩断层摩擦系数随温度变化规律不同:低围压(30 MPa)下,摩擦系数随温度升高先增大后减小,中高围压(≥70 MPa)下摩擦系数则表现为随温度先减小后增大.断层摩擦滑动行为在100~300℃的范围内表现出由稳定的速度强化转化为不稳定的速度弱化,且在400℃左右重新转变为稳定的速度强化.实验后断层滑动面形貌和微观结构分析表明,稳定滑动断层面为高反射镜面,擦痕清晰;黏滑断层面为有光泽的凹凸不平的表面;最高围压下蠕滑的断层面粗糙无光泽,擦痕不可辨别.本文认为受温度激活的塑性变形过程逐步主导了岩石变形,对断层激活发生不稳定滑动至关重要,而高围压则会抑制断层的不稳定滑动.本研究结果不仅为识别野外断层黏滑和蠕滑提供了实验证据,而且为探究强震孕育和发生机理等提供重要的参数.

To explore the mechanical behavior and slip stability of faults,we performed frictional experiments on saw-cut samples of dry Carrara marble using a gas medium triaxial apparatus.The temperatures(T)were 70~400℃in the experiments and the confining pressure(Pc)ranged from 30 to 100 MPa,and the slip velocity(V)was switched among 0.08μm·s^(-1),0.4μm·s^(-1) and 2μm·s^(-1),respectively.The experiments reveal that the temperature dependence of the marble friction varies with the confining pressure in the case of Pc=30 MPa,frictional coefficient increases first and then decreases with temperature in the range of 70 to 400℃;for P_(c)≥70 MPa,frictional coefficient shows an opposite trend.The marble friction shows a transition from initial velocity-strengthening behavior to velocity-weakening behavior at 100~300℃,and then back to velocity-strengthening behavior at around 400℃.Macroscopic morphology and microstructure analysis of postmortem fault surfaces show that stable sliding tends to produce mirror-like surfaces with clear striations;and stick-slip seems to be associated with shiny but bumpy surfaces.In contrast,no visible striation can be found on the slip surfaces of the creeping faults under high confining pressure.These results suggest that crystal plastic deformation process activated by temperature plays a key role in the activation of unstable slip,while high confining pressure may suppress the unstable slip.Our work may shed light on how to identify the slip behaviors of faults(stick slip or creep)in the field and provide new insights into mechanisms of earthquake nucleation at depth.