HR: 17:30h
AN: T14B-07    [Abstracts]
TI: 3D numerical simulations of fault gouge evolution during shear
AU: * Mair, K
EM: karen.mair@fys.uio.no
AF: Physics of Geological Processes, University of Oslo, PO Box 1048 Blindern, Oslo, 0316 Norway
AU: Abe, S
EM: steffen@esscc.uq.edu.au
AF: Earth Systems Science Computational Centre, University of Queensland, St Lucia, Brisbane, QLD 4072 Australia
AB: Fault gouge evolution during shear has been shown to have important implications for fault strength and stability. There remain however key challenges in linking specific grain scale processes to their macroscopic frictional response. Discrete numerical models of granular shear are useful to investigate these processes since they allow a degree of dynamic visualization at the grain scale not easily afforded in the laboratory or field. We present a new method to implement realistic gouge evolution in 3D simulations of granular shear. We use a particle based model that includes breakable bonds between individual particles allowing fracture of large aggregate grains during shear. During faulting simulations, involving the application of a constant normal stress followed by shear at constant velocity, particle motions and interactions as well as mechanical behavior of the entire system are continuously monitored. We show that a model fault gouge initially characterized by monodisperse aggregate grains gradually evolves to a power law size distribution with accumulated strain. Grain shape evolves from initially spherical aggregate grains to a mix of spherical and angular fragments. Some survivor grains maintain near original shapes and grain sizes to relatively high shear strains, clearly buffered by their neighbors. The comminution process yields a textural signature highly indicative of natural and laboratory produced fault gouges. Quantitative results agree well with a constrained comminution model for self-similar fault gouge development and mechanical behavior is comparable to a first order with relevant laboratory data. Importantly, our simulations also reveal a strong correlation between regions of enhanced grain size reduction and localized strain. Thus in addition to producing realistic fault gouge textures, our model offers the possibility to explore direct links between strain partitioning and structural development in fault zones. This could permit investigation of subtle interactions between high and low strain regions that may trigger localization - delocalization events and therefore control macroscopic frictional stability of evolving fault zones.
DE: 0545 Modeling (4255)
DE: 7209 Earthquake dynamics (1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: Fall Meeting 2005