In this study, we use the Discrete Element Method (DEM) to numerically simulate the micromechanics of frictional behavior of faults. Although fault zone widths can be tens of meters, the principal slip occurs within localized zones having widths of a few millimeters. Fault slip analysis is complicated by uncertainties in slip mechanics. Depending on rate and state of slip, the system can undergo weakening or strengthening, however the details of the underlying mechanisms remain uncertain. The DEM can provide a robust modeling tool to capture many micromechanical features present within these fault slip zones that are beyond observation in physical experiments. In this work, we investigated the origin of the rate and state effects under various boundary conditions aiming to improve the representation of rate and state effects in larger-scale continuum analysis. Primary subject of this study is the relationship between stresses occurring at the particle scale and the constitutive response assumed in macro scale analyses.

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