AI 中文总结
研究地震周期中断层带流体压力变化控制因素，通过实验室岩石摩擦实验监测孔隙压力，发现准静态加载和动态滑动时孔隙压力变化规律及偏差，还检测到滑动成核前孔隙压力下降，分析表明孔隙弹性耦合影响断层有效法向应力。
AI 中文摘要
为了阐明地震周期中断层带内影响流体压力变化的主要控制因素，我们进行了实验室岩石摩擦实验，在准静态加载序列后接动态滑动事件的过程中对流体压力进行原位监测。模拟断层是在饱和水的韦斯特利花岗岩圆柱体中呈30°的锯切，在三轴条件下进行测试。孔隙压力在岩块边界保持恒定，但韦斯特利花岗岩的低水力扩散率使断层与边界在水力上断开。在断层锁定的准静态加载过程中，我们观察到孔隙压力增加，解释为断层的孔隙弹性闭合。在动态滑动事件中，孔隙压力系统地下降，下降幅度与法向应力下降相当。孔隙压力下降的很大一部分被解释为断层的孔隙弹性张开。观察到与孔隙弹性效应的偏差：在小事件中，孔隙压力下降比预期的更大，表明非弹性膨胀。在一些大事件中，孔隙压力下降比预期的小，这可能是压实或热增压的迹象。在宏观滑动事件之前，我们检测到孔隙压力系统地下降高达约1MPa，与沿断层的不均匀预滑动的发生相关。通过局部应变计数据的运动学反演推断的滑动成核与1至10μm量级的局部滑动幅度相关，并且似乎导致非弹性膨胀。包括扩容和孔隙弹性效应的断层滑动稳定性分析表明，孔隙弹性耦合倾向于补偿法向应力变化，导致如果条件不排水，断层在基本恒定的有效法向应力下运行。
英文摘要
In order to clarify the main controlling factors influencing fluid pressure changes in fault zones during the seismic cycle, we conducted laboratory rock friction experiments where fluid pressure was monitored in situ during sequences of quasi-static loading followed by dynamic slip events. The simulated fault was a 30$^\circ$ saw-cut in a Westerly granite cylinder, saturated with water, tested under triaxial conditions. Pore pressure was held constant at the boundaries of the block, but the low hydraulic diffusivity of Westerly granite made the fault hydraulically disconnected from the boundaries. During quasi-static loading while the fault was locked, we observed pore pressure increases which we interpret as poroelastic closure of the fault. During dynamic slip events, pore pressure systematically dropped by amplitudes commensurate to the normal stress drop. A large contribution to the pore pressure drop is interpreted as poroelastic opening of the fault. Deviations from the poroelastic effects are observed: in small events, pore pressure dropped further than anticipated, indicating inelastic dilation. In a few large events, pore pressure dropped less than anticipated, which could be the sign of compaction or thermal pressurisation. Prior to macroscopic slip events, we detect systematic pore pressure decreases by up to around 1 MPa, correlated to the occurrence of inhomogeneous preslip along the fault. Slip nucleation, inferred by kinematic inversion of local strain gauge data, is linked to local slip magnitudes of the order of 1 to 10 $μ$m, and appears to lead to inelastic dilation. A stability analysis of fault slip including dilatant and poroelastic effects shows that poroelastic coupling tends to compensate normal stress variations, leading to faults operating under mostly constant effective normal stress if conditions are undrained.
