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

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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.