Parallel 3D Simulation of a Fault Gouge Using The Lattice Solid Model

Despite the insight gained from 2D particle models, and given that the dynamics of crustal faults occur in 3D space, the question remains, how do the 3D fault gouge dynamics differ from those in 2D? Traditionally, 2D modeling has been preferred over 3D simulations because of the computational cost of solving 3D problems. However, modern high performance computing architectures, combined with a parallel implementation of the Lattice Solid Model (LSM), provide the opportunity to explore 3D fault micromechanics and to progress understanding of effective constitutive relations of fault gouge layers. In this paper, macroscopic friction values from 2D and 3D LSM simulations, performed on an SGI Altix 3700 super-cluster, are compared. Two rectangular elastic blocks of bonded particles, with a rough fault plane and separated by a region of randomly sized non-bonded gouge particles, are sheared in opposite directions by normally-loaded driving plates. The results demonstrate that the gouge particles in the 3D models undergo significant out-of-plane motion during shear. The 3D models also exhibit a higher mean macroscopic friction than the 2D models for varying values of interparticle friction. 2D LSM gouge models have previously been shown to exhibit accelerating energy release in simulated earthquake cycles, supporting the Critical Point hypothesis. The 3D models are shown to also display accelerating energy release and good fits of power law time-to-failure functions to the cumulative energy release are obtained.