Lengthscales in avalanche dynamics in sheared granular systems

Under shear, amorphous solids fail via localized particle rearrangements that often coalesce into avalanches, but a microscopic explanation of the dynamics of avalanches has remained out of reach. I will discuss some of our recent work to develop new tools to characterize the dynamics of avalanches and relate them to microscopic structural features. We have used these techniques to quantitatively compare spatiotemporal four-point correlations in the plasticity field during avalanches in both frictionless granular simulations and simulations of coarse-grained elasto-plastic models. We find two length scales: a short "excitable" length scale associated with sites that have finite yield stresses and a large "marginal" length scale associated with sites that have vanishing yield stress. The larger length scale exhibits the same scaling with time in both elasto-plastic and granular simulations, while the short one scales differently in the two systems.