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积聚在地球上的压缩力（应力）。这种应力的积累和释放通常使用将岩石视为类似弹簧的弹性材料的模型来研究。然而，真实的岩石——尤其是那些断层带周围的岩石——含有许多导致非弹性（永久）变形的缺陷。因此，构造板块之间的运动不仅可以由断层滑动调节，还可以由分布在围岩中的变形调节。忽视这些影响可能会导致高估地球上的应力积累。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，研究小组的目标是通过实验室实验来描述这种岩石的行为。他们使用存在缺陷的岩石样品；标本要么在自然断层附近收集，要么在实验室制备。他们量化岩石的行为，并通过数值模拟评估其对地震力学的影响。该项目为威斯康星大学麦迪逊分校的早期职业科学家、研究生和本科生提供支持。它还促进了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带流变学对断层力学的影响。现场和实验室证据表明，断层破坏带岩石表现出随时间变化的变形行为，并且破坏带内的剪切应力松弛是普遍存在的现象。目前的断层力学模型未考虑断层损伤带岩石的粘性特性。这可能导致对断层剪应力积累的高估。在这里，研究人员描绘了选定断裂带露头周围的破坏分布。重点是对断层上和断层上的非均质性进行量化。为了在粘塑性框架下约束损伤岩石的粘性本构特性，对天然和合成损伤区岩石进行了室内试验。综合建模结合了现场和实验室的发现。目的是评估粗糙破坏带的缓慢分布变形如何影响断层剪应力的震间载荷。该小组还研究了地震间期应力分布和断层滑动的演变；这提供了地震统计和运动学如何在地震间加载演变的见解。另一个目标是评估上尺度摩擦定律对现场尺度问题的有效性。最后，将对圣哈辛托断裂带地震速度和应变的瞬态变化进行地球物理观测，以探索与实验室约束的粘性特性的一致性。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.