Dynamic friction in sheared fault gouge: Implications of acoustic vibration on triggering and slow slip

Friction and deformation in granular fault gouge are among various dynamic interactions associated with seismic phenomena that have important implications for slip mechanisms on earthquake faults. To this end, we propose a mechanistic model of granular fault gouge subject to acoustic vibrations and shear deformation. The grain-scale dynamics is described by the Shear-Transformation-Zone theory of granular flow, which accounts for irreversible plastic deformation in terms of flow defects whose density is governed by an effective temperature. Our model accounts for stick-slip instabilities observed at seismic slip rates. In addition, as the vibration intensity increases, we observe an increase in the temporal advancement of large slip events, followed by a plateau and gradual decrease. Furthermore, slip becomes progressively slower upon increasing the vibration intensity. The results shed important light on the physical mechanisms of earthquake triggering and slow slip and provide essential elements for the multiscale modeling of earthquake ruptures. In particular, the results suggest that slow slip may be triggered by tremors.