Collaborative Research: From Loading to Rupture - how do fault geometry and material heterogeneity affect the earthquake cycle?

分析伴随大地震而来的灾害，需要了解构造板块的长期运动与活动断层附近的构造特征之间的相互作用。随着构造板块的移动和变形，板块之间和板块中嵌入的断层(或裂缝)不会滑动，而是由于摩擦阻力而被锁定。随着时间的推移(对于大地震来说是几十年到几百年)，这些断层上的应力增加。当断层上的应力水平超过摩擦阻力时(至少在断层的某些局部区域)，就会发生地震破裂。因此，对整个地震周期(构造加载、成核和破裂的完整演化)进行建模是具有挑战性的，因为它需要许多非常不同的时间尺度的分辨率。其他挑战来自这样一个事实，即断层在几何上很复杂--具有大规模的弯曲和分支以及小规模的非平面特征--并且被包括沉积物和粘土在内的非均质材料以及更坚硬的材料(如花岗岩)所包围。此外，对断层的实地观察显示，大量的裂缝和微裂缝--通常被称为损伤区--必须经常包括在模型中，才能产生现实的结果。在这个项目中，我们将开发、验证和利用地震周期模型，该模型可以严格和自洽地处理复杂的断层几何形状、损伤区和非均质材料。我们还将探索几何形状和非均质性如何影响地震的位置、震级和复发间隔。这项拟议的工作对整个社会都有好处，因为了解复杂性对地震周期的影响直接有助于我们对地震危险性的理解。地震危险性分析需要了解地震周期，包括远程加载和近断层结构的相互作用。目前，没有一个现有的模型可以同时解释具有复杂断层几何形状、不均匀材料和塑性变形的地震间和同震期。这笔资金支持开发和应用一个数值模型，该模型严格考虑了地震间的载荷以及二维和三维的破裂动力学。为了捕捉缓慢构造载荷对应力场演化的影响，将使用计算高效的准静态模型。随着惯性效应变得重要，模型将过渡到完全动态的描述，其中波场及其与断层界面的相互作用被建模。地震周期的所有阶段都将在一个能够捕捉复杂几何和材料描述的自我一致的计算和数学框架中建模。该小组将开发一个并行的准静态和动态破裂建模环境，该环境可以处理复杂的几何形状(例如，分支、弯曲和阶跃)、一般边界条件、塑性变形以及可变的材料和摩擦特性。研究人员将使用开发的模型来考虑几何形状如何影响近断层应力场的形核位置、复发间隔、震级和演化，以及当严格考虑地震周期的所有阶段时，塑性和双材料特性所起的作用。

Analyzing the hazards that accompany large earthquakes requires an understanding of the interplay between the long term motion of tectonic plates and the structural features near active faults. As tectonic plates move and deform, faults (or cracks) between and embedded in the plates do not slide but are locked due to frictional resistance. As time passes (tens to hundreds of years for large earthquakes) the stress on these faults increases. An earthquake rupture occurs when the level of stress resolved on the fault exceeds the frictional resistance (at least in some local region of the fault). Thus modeling the full earthquake cycle (tectonic loading, nucleation, and full evolution of rupture) is challenging because it requires the resolution of many vastly different timescales. Additional challenges arise from the fact that faults are geometrically complex -- with large-scale bends and branches as well as small-scale non-planar features -- and are surrounded by heterogeneous materials including sediments and clays, as well as much stiffer materials such as granite. Furthermore, field observations of faults reveal an abundance of cracks and micro-fractures -- often referred to as a damage zone -- which must often be included in models to produce realistic results. In this project we will develop, validate, and utilize an earthquake cycle model that can rigorously and self-consistently handle complex fault geometries, damage zones, and heterogeneous materials. We will also explore how geometry and heterogeneity affect the earthquake locations, magnitudes, and recurrence intervals. This proposed work benefits the society at large as understanding the impact of complexity on the earthquake cycle directly informs our understanding of seismic hazard.Seismic hazard analysis requires an understanding of the earthquake cycle including the interaction of remote loading and near-fault structure. Currently, no existing models can account for both the interseismic and coseismic periods with complex fault geometries, heterogeneous materials, and plastic deformation. This funding supports the development and application of a numerical model that rigorously accounts for interseismic loading as well as rupture dynamics in both two- and three-dimensions. To capture the effect of slow tectonic loading on the evolution of the stress field, a computationally efficient quasi-static model will be used. As inertial effects become important, the model will transition to a fully dynamic description where the wavefield is modeled along with its interaction with fault interfaces. All stages of the earthquake cycle will be modeled in a single, self-consistent computational and mathematical framework capable of capturing both complex geometries and material descriptions. The group will develop a parallel quasi-static and dynamic rupture modeling environment that handles complex geometries (e.g., branches, bends, and step-overs), general boundary conditions, plastic deformation, and variable material and frictional properties. The investigators will use the developed model to consider how geometry affects nucleation location, recurrence interval, magnitude, and evolution of the near-fault stress field will be studied as well as the role that plasticity and bi-material properties play when all stages of the earthquake cycle are rigorously considered.