Dynamical weakening by fluidization under oscillatory viscous flows

Abstract

AbstractDynamical weakening of granular materials plays a critical role on diverse geological events such as seismic faulting and landslides. A common feature in the dynamics of these processes is the development of fluid‐solid relative flows, which could lead to fluidization by hydrodynamic viscous stresses. This work is focused on analyzing hydrodynamic fluidization under oscillatory viscous flows as a possible driving mechanism for dynamical weakening. The theoretical estimations and experimental observations presented and reviewed suggest that fluidization can be greatly promoted by oscillatory viscous flows, which are usually expected in geological events involving vibration of granular materials in viscous fluids. Fluidization under oscillatory viscous flows may occur at not excessively large vibration velocities of fine particles in gases or relatively larger particles in liquids or supercritical fluids. In particular, the enhancement of fluidization by high‐frequency vibrations would be a powerful mechanism to promote dynamical weakening of fine powders in dry fault gouges, failure of liquid‐ (or supercritical fluid‐) saturated beds, and sustained fluidization of pyroclastic flows and lahars.