Thermodynamics of Fault Slip at Seismic Velocities

与地震滑动相关的热扰动对地震过程中的动摩擦和机械能释放有显著影响。先前的理论工作和现场观察表明，许多温度相关机制，包括微观和宏观熔融，增强塑性和孔隙流体增压，可能会显著改变高滑移速度下的有效断层强度。然而，有效断层摩擦的大小、时空格局，甚至是热致变化的标志都还不清楚。最近，岩石摩擦的实验测量已经扩展到接近每秒米的滑动率。实验数据揭示了有效岩石摩擦对温度、滑动速率和断层-正应力的复杂依赖关系；弱化和强化行为均有报道。也许高速实验室实验中最有趣的发现是，在宏观熔化开始时，摩擦明显增加。这种增加可能表明，在高滑移速度下，基本物理从粗糙接触滑动转变为类似粘性的流动。该项目研究了同震加热对动态断层强度的影响，通过建立一个断层带变形的热力学一致模型，该模型明确包括热传递、相变（例如熔化和冻结）和断层带岩石的现实流变学。用于验证模型预测的观测数据包括对暴露断裂带“精细结构”的现场观测（特别是滑动局部化程度）、伪水晶石脉的形态以及实验室高速滑动实验的新结果。这项工作可能有助于正在进行的关于主要地壳断层活动时的应力大小的讨论

Thermal perturbations associated with seismic slip may significantly affect the dynamic friction and the mechanical energy release during earthquakes. Previous theoretical work and field observations suggestthat a number of temperature-dependent mechanisms, including micro-and macroscopic melting, enhanced plasticity, and pore fluid pressurization may dramatically modify the effective fault strength athigh slip velocities. However, the magnitude, the spatio-temporal patterns, and even the sign of the thermally-induced variations in the effective fault friction are not well known. Recently, experimentalmeasurements of the rock friction have been extended to slip rates approaching the seismic range of meters per second. The experimental data reveal a complex dependence of the effective rock friction ontemperature, slip rate, and fault-normal stress; both weakening and strengthening behavior is reported. Perhaps the most intriguing finding of the high-speed laboratory experiments is an apparentincrease in friction upon the onset of macroscopic melting. This increase may indicate a change in the basic physics from the asperity-contact sliding to a viscous-like flow at high slip velocities. This project investigates effects of the co-seismic heating on the dynamic fault strength by developing a hermodynamically consistent model of the fault zone deformation that explicitly includes heat transfer, phase transitions (e.g., melting and freezing), and realistic rheology of the fault zone rocks. Observables used to validate the model predictions include field observations of the "fine structure'' of the exposed fault zones (in particular, the degree of slip localization), morphology of the pseudotachylite veins, and new results from the laboratoryhigh-speed sliding experiments. This work may contribute to the on-going discussion about the magnitude of stress at which the major crustal faults operate.--