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。该项目特别关注的是由于断层不仅可能在断层面本身滑动，而且周围的受损岩石也可能变形以适应板块运动而产生的复杂性之一。​更好地理解这些现象将阐明当前地震断层模型中仍然缺乏的东西，并提高地震危险性分析的准确性。该计划也将透过与台湾科学家的紧密研究合作，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，这对培养将在国际合作环境中工作的下一代科学家至关重要。本研究的目的是表征断裂损伤带岩石的韧性变形特性，并评价这种行为在断层力学中的重要性。大多数解析和数值断层力学模型将断层视为嵌入在弹性主岩之间的摩擦界面，而没有考虑到断层面周围损伤带的特殊特征。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，这对地震间期断层上的剪切应力如何发展具有重要影响。该项目的重点是台湾的车隆堡断层，在那里从2004年的国际大陆钻探项目中回收了高质量的岩心材料。以断裂密度为重点，详细描述车隆堡断裂系统的断裂破坏带，然后进行蠕变实验，利用破坏带样品测量随时间变化的应变行为。利用实验室推导的本构方程，评估构造条件下损伤区的变形行为。将韧性本构律与断层摩擦特性结合在一个数值模型中，量化地震构造加载过程中各域、损伤带和断层核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尺度上（超过一年）发生。例如，如果从大地测量学研究中推断出的俯冲界面的部分耦合确实是由于稳定的离断层变形造成的，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.