Thermodynamics of Fault Slip at Seismic Velocities

与地震滑移相关的热扰动可能会显着影响地震期间的动摩擦和机械能释放。先前的理论工作和现场观察表明，许多与温度相关的机制，包括微观和宏观熔化、增强的塑性和孔隙流体加压，可能会显着改变高滑移速度下的有效断层强度。然而，有效断层摩擦热引起的变化的大小、时空模式，甚至符号尚不清楚。最近，岩石摩擦的实验测量已扩展到接近每秒米的地震范围的滑移率。实验数据揭示了有效岩石摩擦力对温度、滑移率和断层正应力的复杂依赖性；弱化和强化行为都有报道。也许高速实验室实验中最有趣的发现是宏观熔化开始时摩擦力明显增加。这种增加可能表明基本物理学从粗糙接触滑动到高滑动速度下的粘性流动的变化。该项目通过开发断层带变形的热流动力学一致模型来研究同震加热对动态断层强度的影响，该模型明确包括传热、相变（例如熔化和冻结）以及断层带岩石的实际流变学。用于验证模型预测的观测数据包括对裸露断层带“精细结构”的现场观测（特别是滑动定位的程度）、假速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关于主要地壳断层运行时的应力大小的持续讨论。

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.--