Dilatancy-induced fluid pressure drop during dynamic rupture: Direct experimental evidence and consequences for earthquake dynamics
Dilatancy-induced fluid pressure drop during dynamic rupture: Direct experimental evidence and consequences for earthquake dynamics
复制标题
DOI：
10.1016/j.epsl.2020.116179
复制
发表时间：
2020-05-15
影响因子：
5.3
通讯作者：
Brantut, Nicolas
中科院分区：
文献类型：
--
作者：
Brantut, Nicolas
流体压力和地壳流动是控制地震物理的关键参数。由于地震滑动与形变的时空局部化有关，预计断层面周围的局部流体压力可能会潜在地影响滑动断裂带的动态强度。从实地研究中已经推断出同震流体压力下降，特别是在被认为是由这一过程形成的金矿床中，但仍然缺乏可靠的定量预测。文中给出了在上地应力条件下动态岩石破裂和摩擦滑动过程中断层上和断层外局部流体压力变化的实验结果。在主破裂期间，断层流体压力迅速降至零，表明部分汽化和/或脱气。进一步的变形产生了粘滑事件，系统地与流体压力的近瞬时下降有关，为“地震吸力泵”的概念提供了直接的实验支持。现场流体体积和波速测量结合显微构造研究表明，在破裂和滑动过程中，扩容是驱动流体压力下降的过程。实验室结果的外推表明，膨胀引起的流体压力下降可能是地壳中的一种普遍现象，抵消了热压力作为新破裂岩石中的一种削弱机制。(C)2020爱思唯尔B.V.保留所有权利。
Fluid pressure and flow in the crust are key parameters controlling earthquake physics. Since earthquake slip is linked to spatio-temporal localisation of deformation, it is expected that the local fluid pressure around the fault plane could potentially impact the dynamic strength of the slipping fault zone. Coseismic fluid pressure drops have been inferred from field studies, notably in gold deposits which are thought to be formed by this process, but reliable quantitative predictions are still lacking. Here, experimental results are presented where local on- and off-fault fluid pressure variations were measured in situduring dynamic rock fracture and frictional slip under upper crustal stress conditions. During the main rupture, the on-fault fluid pressure dropped rapidly to zero, indicating partial vaporisation and/or degassing. Further deformation produced stick-slip events systematically associated with near-instantaneous drops in fluid pressure, providing direct experimental support of the concept of "seismic suction pump". In situ fluid volume and wave speed measurements together with microstructural investigations show that dilatancy is the process driving fluid pressure drops during rupture and slip. Extrapolation of the laboratory results indicate that dilatancy-induced fluid pressure drops might be a widespread phenomenon in the crust, counteracting thermal pressurisation as a weakening mechanisms in freshly fractured rock. (C) 2020 Elsevier B.V. All rights reserved.