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.