Rheology of Nano-Crystalline and Amorphous Materials

Strain localization into fine grained zones is ubiquitous. What is the minimal grain size rocks can achieve? Improvements in resolution of electron microscopes  and advances in sample preparation have lead to the discovery that nanocrystalline and  amorphous materials are abundant in both nature as well as experiments under a broad range of conditions.  Nano-crystalline materials are surface-dominated, i.e. more atoms form the surface than the interior of a grain, and their rheological behavior is distinct from micro-crystalline materials which are volume dominated, i.e. most atoms form the interior of a grain. Amorphous materials do not have any grain size per-se as coherent zones of long range order (i.e. crystallinity) are absent. Understanding the rheological behavior of nano-crystalline and amorphous materials in the context of faults offers new insights into mechanisms which can lead to rapid strain transients that can cause earthquakes.