The importance of the third dimension in granular shear

We present new numerical results showing the importance of the third dimension in simulations of granular shear. Our 3‐D numerical models of gouge layers under shear exhibit friction levels notably higher than 2‐D models and values that approach those of recent laboratory experiments on spherical beads. Fluctuations in friction are directly related to grain reorganization normal to shear. In 3‐D, these fluctuations are reduced due to significant particle motion in the third dimension, leading to a steady frictional sliding curve. Since these fluctuations are small compared with 2‐D models, our 3‐D simulation offers potential to investigate small amplitude but extremely important second order rate and state friction effects that fundamentally control the strength and stability of fault zones.