Three-Dimensional Distinct Element Simulations of Dynamic Process of Fault Gouge Evolution

脆性断裂带在滑动过程中不断受到断层表面的磨损，导致断层表面粗糙度不断变化，断层泥带厚度逐渐增加，产生净滑动。断层泥特征的动态变化可能影响断层的摩擦强度、稳定性和地震特征。尽管以往的野外、实验室和数值研究在研究断层泥带的几何和物理性质及其对断层带摩擦和力学行为的影响方面取得了重大进展，但这些结果仍然有助于理解在更大范围的地质背景下泥带发育的全过程，以及这些材料如何影响地震周期。最近对离散单元法(DEM)的修改，包括增加了粒间粘结和断裂，使我们能够模拟粘性岩石的破裂过程，并使直接观察泥的堆积和改造，模拟天然断裂带的变形成为可能。二维DEM对断层带演化的模拟已经成功地再现了野外和实验室中的许多观测结果，得到了以前的断层带研究中没有报道的有趣的发现。这些阶段包括泥层带的发展阶段及其对剪切位移、正应力和岩石强度的依赖。这些令人鼓舞的结果表明了改进数值模型的可行性、必要性和重要性，并将当前的研究扩展到未来。本方案描述了一个模拟断层泥演化动态过程的程序，重点是约束断层泥厚度、粒度分布、剪切区强度和表面粗糙度之间的关系。我们将使用更大的组合，允许更大范围的表面和颗粒大小和几何，并在新的莱斯·克雷XD1超级计算机上并行进行这些模拟。这些数值实验的结果将有助于解释对更复杂的自然断层的观测，导致对断裂带过程的更好的理解。这项工作将支持博士后助理本科生的培训，并为社区提供增强的断层泥演化的3D代码。了解断裂带是如何变形的，有助于提高对断层如何滑动从而造成地震危害的理解。

Brittle fault zones undergo continual wear of fault surfaces during slip, whichleads to a continuous variation in fault surface roughness and a progressive increase inthe thickness of the fault gouge zone with net slip. The dynamic changes in gouge zonefeatures may affect fault frictional strength, stability, and earthquake characteristics.Although previous field, laboratory, and numerical studies have made significantprogress in investigating the geometrical and physical properties of fault gouge zones andtheir effects on fault zone frictional and mechanical behavior, these results still providelimited understanding of the complete process of gouge zone development under a widerange of geological settings, and how these materials might affect the earthquake cycle.Recent modifications to the Distinct Element Method (DEM), including additionof interparticle bonding and breakage, allows us to model the fracture process of cohesiverocks, and makes it possible to directly observe gouge accumulation and modification,mimicking natural fault zone deformation. 2-D DEM simulations of gouge evolutionhave successfully reproduced many observations in the field and laboratory, yieldinginteresting findings that have not been reported in previous gouge zone studies. Theseinclude stages of gouge zone development and their dependence on shear displacement,normal stress, and rock strength. These encouraging results suggest the feasibility,necessity, and importance of improving numerical models and extending the currentstudies into the future.This proposal describes a program to simulate the dynamic processes of gougezone evolution, focused on constraining the relationships between gouge thickness, grainsize distribution, shear zone strength, and surface roughness. We will use much largerassemblages that will allow a wider range of surface and particles sizes and geometries,and conduct these simulations in parallel on the new Rice Cray XD1 supercomputer.Results of these numerical experiments will help in interpreting observations of morecomplex natural faults, leading to an improved understanding of fault zone processes.The work will support training of a postdoctural associate, undergraduates, and provide enhanced 3D codes of fault gouge evolution to the community. Understanding how fault zonesdeform can help improve understanding of how faults slip and thus earthquake hazards.