岩盐断层带摩擦滑动的速度依赖性转换及其地震学意义

为了深入理解断层带摩擦滑动速度依赖性转换及其机制,利用双轴摩擦实验对干燥及含水条件下岩盐断层带摩擦的速度依赖性进行了实验研究,并观测了摩擦滑动过程中的声发射,分析了断层带的微观结构.实验结果表明,干燥岩盐断层带在0.1~100 μm/s的速度范围内表现为速度弱化,增大σ₂会使断层带向速度强化转变;含水条件下岩盐断层带在1~100 μm/s的速度范围内表现为速度弱化,而在0.1~0.01 μm/s的速度范围内表现为速度强化,速度依赖性转换出现在0.1~1 μm/s,其中断层表现为振荡或应力释放时间较长的黏滑事件;岩盐断层带在干燥条件下表现出很强的声发射活动,每个黏滑均对应一丛声发射事件,而在含水条件下一次黏滑只对应一个声发射事件.显微观察表明,局部化的脆性破裂是速度弱化域的主要变形机制,分布式的碎裂流动是干燥岩盐断层带在速度强化域的变形机制,颗粒边界迁移以及压溶作用的塑性变形是含水条件下岩盐断层带在速度强化域的主要变形机制,而脆性破裂和塑性变形共同控制着速度依赖性转换域断层带的变形.水的存在促进岩盐发生塑性变形,进而导致断层带从速度弱化向速度强化转换.上述结果有助于理解断层带上地震活动的特征和慢地震的机制.

Velocity-dependence transition of friction for halite gouge and its significance implication in seismology

In order to better understand the velocity-dependence of fault frictional sliding and its mechanism, the velocity-dependence of friction for dry and wet halite gouge was studied by using biaxial friction configuration, the acoustic emission produced during the frictional sliding was recorded, and the microstructure of gouge zone was observed. The experiments show that dry halite gouge behaves velocity weakening at the velocity of 0.1~100 μm/s, and increasing σ₂ can enhance the transition to velocity strengthening. Wet halite gouge behaves velocity weakening at high velocity of 1~100 μm/s and velocity strengthening at low velocity of 0.1~0.01 μm/s, and the velocity-dependence transition occurs at velocity of 0.1~1 μm/s and behaves oscillation or stick-slip with much longer time than that in the velocity weakening region. Dry halite gouge shows strong acoustic emission (AE) activity and each stick-slip event corresponds to a cluster of AE events, while each stick-slip event is accompanied by only one AE event for wet halite gouge. The microscope observation indicates that localized brittle deformation is predominant in the velocity weakening region, and distributed cataclastic flow is the mechanism in the velocity strengthening region for dry halite gouge, while plastic deformation including grain boundary migration and pressure solution is predominant in the velocity strengthening region for wet halite gouge. Additionally, both brittle deformation and plastic deformation exist in the transitional region. The existence of water enhances the plastic deformation of halite gouge and thus causes the transition from velocity weakening to velocity strengthening. The results described above are helpful for understanding seismicity along fault zone and mechanism of slow earthquakes.