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

Abstract

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.

Localization and instability in sheared granular materials: Role of friction and vibration

“…This is consistent with the findings of Lieou et al [17,25]. However, due to the strain localization in our simulations the stick-slip is only confined to the banded domain.…”

“…While shear induced dilation has been coined as rate strengthening, the non-montonic volume response in the presence of vibration points to possible transition into rate weakening and accordingly loss of sliding stability. This has been successfully demonstrated by Lieou et al [17,25] who explored stick-slip dynamics under a wide range of strain rates and confining pressures and discovered a transition from fast stick-slip to slow stick-slip and ultimately stable sliding as a function of increasing vibration intensity. However, in these previous studies it was observed that the stability properties before the application of external vibrations are recovered upon cessation of vibration and apparently no lasting rheological changes occurred.…”

“…The theory was recently modified by [25] to incorporate the effects of external vibration on a sheared layer with spatially homogeneous structure. In this paper, we extended this model by allowing the possibility that the spatial distribution of the compactivity or porosity in the granular layer is non-uniform.…”

“…For one thing, stick-slip becomes apparent. Previous studies by Lieou et al [17,25] on shearing a spatially homogeneous granular layer suggested stick-slip is possible only in the presence of friction. This is still the case even when shear bands form.…”

Simulating stick‐slip failure in a sheared granular layer using a physics‐based constitutive model

“…(If the granular layer is subjected to external vibration, there is an extra term corresponding to the rate at which vibration pumps energy into the system. This term can be neglected if we restrict our analysis to an unvibrated granular layer [ Lieou et al , ]). The latter is encapsulated in the transport coefficient , which must be nonnegative because of the second law of thermodynamics; it includes dissipation due to inelastic collisions and friction between grains.…”