Size polydispersity tunes slip avalanches of granular gouge

Granular materials are ubiquitous in nature and important to a wide range of industrial processes. When driven at slow rates, granular materials deform via intermittent dynamics which alternates slow elastic loading with rapid slips. Such serrated behaviors have attracted attentions from researchers in material science, process engineering and powder technology. They have aroused great interest for geoscientists since key clues may be offered for the origin of earthquake physics. The avalanche-like slip events of granular materials reveal a strong statistical similarity with earthquakes, having made granular materials widely adopted as an ideal laboratory model material for the study of earthquake physics. Different granular systems subjected to different loading conditions present similar scaling laws, such as the power-law distributions of event size. However, the scaling exponents describing avalanche distributions vary greatly in range, posing challenges to the existence of universal scaling across diverse granular systems. In this study, we examined granular systems with varying size polydispersity from mono-sized spheres to highly polydisperse pickings and found the signature of tunable avalanche statistics. We further use size polydispersity as a control parameter to generate continuously adjustable avalanche statistics.