CAREER: Mechanics of Viscous Damage Zones Along Rough Faults and Community Tutorial/Forums for Experimental Rock Mechanists

地震的发生是为了释放由于板块构造而在地球中积累的压缩力（应力）。这种应力的积累和释放经常使用将岩石视为弹簧状弹性材料的模型来研究。然而，真实的岩石--尤其是断层带周围的岩石--包含许多导致非弹性（永久）变形的缺陷。因此，构造板块之间的运动不仅可以通过沿着断层的滑动来调节，而且还可以通过分布在围岩中的变形来调节。忽视这些影响可能会导致高估地球的应力积累。 因此，考虑断层周围的岩石变形对于准确评估地震危险性至关重要。在这里，该团队的目标是通过实验室实验来描述这种岩石行为。他们使用存在缺陷的岩石标本;标本要么在天然断层周围收集，要么在实验室制备。他们量化岩石行为，并通过数值模拟评估其对地震力学的影响。该项目为威斯康星州-麦迪逊大学的一位早期职业科学家、研究生和本科生提供支持。它还促进岩石力学实验专家之间的知识转移和社区建设。该项目的目标是评估断层损伤区流变学对断层力学的影响。现场和实验室的证据表明，断层损伤区岩石表现出时间依赖性的变形行为和剪切应力松弛损伤区内是一个普遍存在的现象。断层损伤带岩石的粘性特性在现有的断层力学模型中没有得到承认。这可能导致对断层剪应力积累的高估。在这里，研究人员描述了选定的断层带露头周围的损害分布。重点是量化跨断层和沿着断层的非均质性。通过对天然和人工合成损伤区岩石的实验研究，将损伤岩石的粘性本构特性约束在粘塑性框架内。一个综合模型结合了现场和实验室的研究结果。其目的是评估如何缓慢分布的变形在粗糙的损伤区影响断层剪切应力的震间加载。该团队还研究了地震期间应力和断层滑动的分布如何演变;这为地震统计和运动学如何在地震加载期间演变提供了见解。另一个目标是评估的有效性，现场规模的问题的升尺度摩擦定律。最后，将对来自圣哈辛托断层带的地震速度和应变的瞬态变化的地球物理观测进行检查，以探索与实验室中限制的粘性特性的一致性。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Earthquakes occur to release the compressional forces (stress) that accumulate in the Earth due to plate tectonics. Such accumulation and release of stress is oftentimes studied using models that treat rocks as spring-like elastic materials. However, real rocks - especially those surrounding fault zones - contain many defects that cause non-elastic (permanent) deformation. Therefore, movement between tectonic plates may not only be accommodated by slip along faults, but also by deformation distributed in the surrounding rocks. Ignoring such effects may lead to overestimating stress accumulation in the Earth. Accounting for rock deformation around faults is thus crucial to accurately assess seismic hazards. Here, the team aims to characterize such rock behavior through laboratory experiments. They use rock specimens with existing defects; specimens are either collected around natural faults or prepared in the laboratory. They quantify the rock behavior and assess its impact on earthquake mechanics through numerical modeling. The project provides support for an early-career scientist and graduate and undergraduate students at University of Wisconsin - Madison. It also fosters knowledge transfer and community building among experimentalists experts in rock mechanics.The goal of the project is to evaluate the impact of fault damage-zone rheology on fault mechanics. Field and laboratory evidence shows that fault damage-zone rocks exhibit time-dependent deformational behavior and that shear stress relaxation within the damage zone is a ubiquitous phenomenon. Viscous properties of fault damage-zone rocks are not acknowledged in current fault mechanical models. This may lead to an over-estimation of fault shear stress accumulation. Here, the researchers characterize the damage distribution around selected fault zone outcrops. The emphasis is on quantifying the heterogeneities across and along the faults. Laboratory experiments are conducted on both natural and synthetic damage-zone rocks to constrain the viscous constitutive properties of damaged rocks in the framework of viscoplasticity. A synthesis modeling incorporates findings from the field and lab. The goal is to evaluate how slow distributed deformation in rough damage zones influence the interseismic loading of fault shear stress. The team also examines how the distribution of stress and fault slip evolve during the interseismic period; this provides insights on how earthquake statistics and kinematics evolve during interseismic loading. Another goal is to evaluate the validity of upscaling friction laws to field scale problems. Finally, geophysical observations on transient changes in seismic velocity and strain from the San Jacinto Fault Zone will be examined to explore consistency with the viscous properties constrained in the laboratory.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.