Bulk rheology of fault damage zone materials and its implication for interseismic fault mechanics

该项目旨在更好地了解导致主要板块边界破坏性地震的构造加载过程。过去十年的进展使科学家能够捕捉和模拟地震周期的一阶特征，但在理解地震现象的随机性和空间变异性方面仍然存在挑战。这个项目特别关注可能出现的复杂性之一，因为断层不仅可能在断裂面本身滑动，而且周围受损的岩石也可能变形以适应板块运动。该项目是与台湾国立中央大学的研究人员合作进行的，包括对台湾车龙铺断层的损伤区样本进行表征，以及对这些样本进行形变实验，以探索损伤区在应力下的行为。对这些现象的更好理解将阐明当前地震断层模型中仍然缺乏的东西，并导致地震危险性分析的准确性提高。该项目还将通过与台湾科学家的强大研究合作，以及研究生交流科学思想和文化经验的机会，促进预期的社会成果，这些交流对于培养未来一代将在国际合作环境中工作的科学家至关重要。本研究的目的是表征断层破坏带岩石的韧性变形特性，并评估这种行为在断层力学中的重要性。大多数分析和数值断层力学模型将断层视为嵌入弹性主岩之间的摩擦界面，而没有考虑断层面周围损伤区的特殊特征。然而，即使在地壳条件下，损伤带岩石也可能发生随时间变化的韧性变形，这对地震间隔期断层上剪应力的发展具有重要影响。该项目的重点是台湾车龙埔断层，在那里，从2004年国际大陆钻探项目中回收了高质量的岩心材料。将详细描述车龙堡断裂系统中的断层损伤区，重点是裂缝密度，然后使用损伤区样本进行蠕变实验，以测量随时间变化的应变行为。使用实验室导出的本构方程，将评估破坏带在构造条件下的变形行为。在数值模型中，将韧性本构关系与断层摩擦特性相结合，以量化在地震间构造加载过程中，各区域、损伤带和断层核心对断层总变形的相对贡献。许多地球物理观测表明，永久的断层外变形可能会在很长的时间范围内(超过一年)发生。例如，如果大地测量研究推断的俯冲界面的部分耦合确实是由于稳定的断层外变形，那么这项研究可能会影响对地震间构造加载过程中应力积累过程的理解。

This project aims to better understand the tectonic loading process leading to devastating earthquakes in major plate boundaries. Advances in the past decade allows scientists to capture and simulate first-order characteristics of the earthquake cycle, but challenges remain in understanding the randomness and spatial variability of earthquake phenomena. This project specifically focuses on one of the complexities that may arise due to the fact that faults may not only slip at the very fault plane itself, but the surrounding damaged rock can also deform to accommodate plate motion. The project, carried out in collaboration with researchers from National Central University, Taiwan, involves characterization of damage zone samples from the Chelungpu fault, Taiwan, coupled with deformation experiments on those samples to explore the behavior of the damage zone under stress. Better understanding of such phenomena will illuminate what is still lacking in current earthquake fault models and lead to improved accuracy of seismic hazard analyses. The project would also advance desired societal outcomes through a strong research collaboration with Taiwanese scientists plus the opportunity for graduate students to exchange scientific ideas and cultural experiences essential to foster future generation of scientists who will work in an international collaborative environment.The objective of this study is to characterize the ductile deformational properties of fault damage zone rocks and to evaluate the importance of such behavior on fault mechanics. Most analytical and numerical fault mechanics models treat faults as a frictional interface embedded between elastic host rocks and does not take into account the peculiar characteristics of the damage zone surrounding the fault plane. However, damage zone rocks may undergo time-dependent ductile deformation even under crustal conditions, which has significant consequences on how shear stress develops on a fault during the interseismic period. The project focuses on the Chelungpu fault, Taiwan, where the high-quality core material was recovered from the 2004 International Continental Drilling Project. Detailed description of the fault damage zones in the Chelungpu fault system will be made with emphasis on fracture density, followed by creep experiments using damage zone samples to measure time-dependent strain behavior. Using lab-derived constitutive equations, deformation behavior of the damage zone under tectonic conditions will be evaluated. The ductile constitutive law will be combined with fault frictional properties in a numerical model to quantify the relative contribution of each domains, damage zone and fault core, to the total fault deformation during interseismic tectonic loading. Many geophysical observations suggest that permanent off-fault deformation may be occurring over long time scales (greater than a year). If, for instance, the partial-coupling of subduction interfaces inferred from geodetic studies is indeed due to steady off-fault deformation, the study may impact understanding of the stress accumulation process during interseismic tectonic loading.