Thermodynamics of Fault Slip at Seismic Velocities

与地震滑动有关的热扰动对地震过程中的动摩擦和机械能释放有重要影响。以前的理论工作和现场观察表明，一些温度依赖的机制，包括微观和宏观熔化，增强塑性，孔隙流体增压可能会显着修改的有效故障强度ahigh滑动速度。然而，在有效的断层摩擦的大小，时空模式，甚至是热引起的变化的迹象并不为人所知。最近，岩石摩擦力的实验测量已经扩展到接近每秒米的地震范围的滑动速率。实验数据揭示了一个复杂的依赖性的有效岩石摩擦对温度，滑动速率，和断层正应力，削弱和加强行为的报告。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的明显增加。这种增加可能表明，在基本的物理变化，从凹凸接触滑动粘性流在高滑移速度。该项目通过开发一个热力学一致的断层带变形模型来研究同震加热对动态断层强度的影响，该模型明确包括热传递、相变（例如，融化和冻结），以及断层带岩石的真实流变学。用于验证模型预测的观测数据包括对暴露断层带的"精细结构"（特别是滑动局部化程度）、假玄武玻璃岩脉的形态以及实验室高速滑动实验的新结果的实地观测。这项工作可能有助于正在进行的关于主要地壳断层活动的应力大小的讨论。

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.--