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

合作研究：从加载到破裂——断层几何形状和材料异质性如何影响地震周期？

• 批准号: 1547603
• 负责人: Brittany Erickson
• 金额: $ 24.18万
• 依托单位: Portland State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-15 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1547603&HistoricalAwards=false
• 关键词: Collaborative; Research; Loading; Rupture; how

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.

分析伴随大地震的危害需要了解构造板的长期运动与活动断层附近的结构特征之间的相互作用。当构造板移动和变形时，板中和嵌入板之间的断层（或裂纹）不会滑动，而是由于摩擦电阻而被锁定。随着时间的流逝（大地震发生数十年至数十年），这些断层的压力增加。当断层上的应力水平超过摩擦电阻时（至少在断层的某些局部区域）时，地震破裂就会发生。因此，建模全地震循环（构造负载，成核和破裂的全部演变）是具有挑战性的，因为它需要分辨出许多截然不同的时间尺度。其他挑战是由于断层在几何上复杂的事实 - 大规模的弯曲和分支以及小规模的非平面特征 - 并被包括沉积物和粘土在内的异质材料以及花岗岩等较硬的材料所包围。此外，故障的现场观察表明，大量的裂纹和微裂缝（通常称为损伤区）通常必须包含在模型中才能产生逼真的结果。在这个项目中，我们将开发，验证和使用地震循环模型，该模型可以严格和自愿处理复杂的断层几何，损坏区域和异质材料。我们还将探讨几何和异质性如何影响地震位置，大小和复发间隔。这项拟议的工作使社会对社会有所帮助，因为了解复杂性对地震周期的影响直接介绍了我们对地震危害的理解。地震危害分析需要了解地震周期，包括远程载荷和近场结构的相互作用。当前，没有现有模型可以用复杂的断层几何形状，异质材料和塑性变形来解释跨界和coseis震动时期。这项资金支持了一个数值模型的开发和应用，该模型严格地说明了两次和三维和三维的破裂动态。为了捕获缓慢的构造负荷对应力场演变的影响，将使用计算有效的准静态模型。随着惯性效应变得重要，该模型将过渡到完全动态的描述，在该描述中，在波场与故障接口的相互作用一起建模。地震循环的所有阶段将以一个自吻的计算和数学框架进行建模，能够捕获复杂的几何形状和材料描述。该组将开发平行的准静态和动态破裂建模环境，该环境处理复杂的几何形状（例如，分支，弯曲和渐进式），一般边界条件，塑性变形以及可变材料和摩擦特性。研究人员将使用开发的模型来考虑几何形状如何影响成核位置，复发间隔，大小和近磨损应力场的演变以及当严格考虑地震循环的所有阶段时，可塑性和双重特性的作用。