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The Structure Lab has a new paper in press titled The effect of a liquid phase on force distribution during deformation in a granular system. Look for it in the Journal of Geophysical Research – Solid Earth.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JB019771

Abstract

Two‐phase systems, where one phase is solid and the other fluid, are widespread in nature. Examples include reservoir rocks holding vital fluids like water or petroleum, slurries of partially crystallized magmas, fluids migrating along faults filled with fault gouge, and even the semi‐brittle crust. Previous studies of two‐phase systems have shown that the fluid phase plays an important role in deformation localization and dynamics (e.g., Higashi and Sumita, 2009; Reber et al., 2014). Here, we present results from experiments investigating the influence of a fluid phase on force distribution in a granular media during simple shear. We use photoelastic polyurethane discs as the granular or solid phase and a linear‐viscous silicone as the fluid phase. The photoelastic property of the discs allows for direct observation and measurement of force magnitude and distribution. We compare the two‐phase experiments to granular experiments without silicone. The addition and percentage of the fluid phase has a strong impact on the force distribution and the overall force chain orientations. In the two‐phase system, the force chains form parallel to the shear plane and only rotate to the principal stress direction with an increase in strain. Locally the fluid phase can support forces and terminate force chains over an extended period of time. Our results are in line with findings from numerical studies investigating the formation of slow slip events, proposing that these events are the result of dynamic interactions between solid and viscous phases.