Three Windows in Stress from the Geology of Faults

断层上的绝对应力的知识对于理解地震是至关重要的，因为它已被证明是难以测量的。这个项目的目标是通过测量断层表面几何形状引起的应力扰动的响应来估计绝对应力。断层周围的地质特征记录了露头中的这种应力扰动，包括主岩（损伤区）中的强烈开裂、断层表面上的条纹和熔融岩石。近年来，在总结断层总位移、地表粗糙度和损伤之间的相互关系方面取得了重大进展。在这个项目中，通过对沿走向变化的详细观察，将地表几何形状和断层特征直接联系起来。这些变化提供了地表不规则性对断层周围应力场扰动程度的测量。更具体地说，研究人员将：（1）测量粗糙和光滑断层或断层部分周围的拉伸断裂模式，并使用此测量来计算近场断层外应力场;（2）测量条纹偏离断层表面凸起的偏转，并使用此测量来计算相对于扰动应力的背景应力;（3）测量假玄武玻璃中与断层几何形状有关的沿走向的变化，并使用该测量来计算摩擦力的界限。了解断层上的应力对于从基于物理的模型计算风险所需的水平上了解地震是至关重要的。该项目旨在通过关注地质断层中记录的证据来填补这一知识空白。这种结合建模和实地考察的策略承诺的结果，可以转移到地震物理学的其他领域。

Knowledge of the absolute stress on faults is as essential to understanding earthquakes as it has proven elusive to measure. The goal of this project is to estimate absolute stress by measuring the response to a stress perturbation caused by fault surface geometry. Geologic features surrounding faults record this stress perturbation in outcrop and include intense cracking in the host rock (damage zones), striations on fault surfaces, and melted rock. Recently, significant progress in generalizing the interrelationships among total fault displacement, surface roughness and damage. In this project surface geometry and fault features are directly linked through detailed observations of along-strike variations. These variations provide measures of how much the surface irregularities perturbed the stress field around the fault. More specifically, the researchers will: (1) measure tensile fracture patterns surrounding rough and smooth faults or sections of faults and use this measurement to calculate the near-field off-fault stress field; (2) measure the deflection of striations away from bumps on fault surfaces and use this measurement to calculate the background stress relative to the perturbing stress; and (3) measure the along-strike variation in pseudotachylyte in relation to fault geometry and use this measurement to calculate a bound on friction.Understanding the stress on faults is critical for understanding earthquakes at the level necessary to calculate risk from a physics-based model. This project is designed to fill in this knowledge gap by focusing on the evidence recorded in geological faults. This combined modeling and fieldwork strategy promises results that can be transferable to other fields of earthquake physics.