Influence of Grain-Scale Properties on Localization Patterns and Slip
Weakening within Dense Granular Fault gouges
Abstract
Fault zones are usually composed of a granular gouge, coming from the
wear material of previous slips, which contributes to friction
stability. Once considering a mature enough fault zone that has already
been sheared, different types of infill materials can be observed, from
mineral cementation to matrix particles that can fill remaining pore
spaces between clasts and change the rheological and frictional
behaviors of the gouge. We aim to understand and reproduce the influence
of grain-scale characteristics on slip mechanisms and gouge rheology
(Riedel bands) by employing the Discrete Element Method. A 2D-direct
shear model is considered with a dense assembly of small polygonal cells
of matrix particles. A variation of gouge characteristics such as
interparticle friction, gouge shear modulus or the number of particles
within the gouge thickness leads to different Riedel shear bands
formation and orientation that has been identified as an indicator of a
change in slip stability (Byerlee et al., 1978). Interpreting results
with slip weakening theory, our simulated gouge materials with high
interparticle friction or a high bulk shear modulus, increase the
possible occurrence of dynamic slip instabilities (small nucleation
length and high breakdown energy). They may give rise to faster
earthquake ruptures.