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.颗粒材料（granular materials）在自然界中无处不在，且对诸多工业过程具有重要应用价值。当以低速驱动时，颗粒材料通过间歇性动力学行为发生变形，该过程表现为缓慢的弹性加载与快速滑移交替进行。这种锯齿状行为吸引了材料科学、过程工程及粉体技术领域研究者的广泛关注。同时，该现象还引发了地球科学家的浓厚兴趣，因为其或可为地震物理学的起源提供关键线索。颗粒材料的类雪崩滑移事件与地震表现出极强的统计相似性，这使得颗粒材料被广泛用作研究地震物理学的理想实验室模型材料。不同加载条件下的各类颗粒系统均呈现出相似的标度律，例如事件规模的幂律分布。然而，描述滑移分布的标度指数在取值范围上差异显著，这为不同颗粒系统间是否存在通用标度性带来了挑战。在本研究中，我们对尺寸多分散性各异的颗粒系统展开了考察，系统范围涵盖从单分散球体到高度多分散的颗粒填充体系，并发现了可调控的雪崩统计特征。我们进一步以尺寸多分散性作为控制参数，生成了连续可调的雪崩统计特性。