Destabilization of long-wavelength Love and Stoneley waves in slow sliding

TL;DR

This paper demonstrates that slow sliding can destabilize long-wavelength Love and Stoneley waves due to frictional effects, leading to instabilities that can propagate at shear wave speeds, challenging previous assumptions about slow slip stability.

Contribution

It reveals that friction-induced destabilization of interfacial waves occurs in slow sliding, with implications for understanding fault slip and interfacial wave behavior.

Findings

Long wavelength interfacial waves are destabilized by friction during slow sliding.

Instabilities can propagate at shear wave speeds even at low slip rates.

Quasi-static approximation is invalid for interfacial wave instabilities in slow slip.

Abstract

Love waves are dispersive interfacial waves that are a mode of response for anti-plane motions of an elastic layer bonded to an elastic half-space. Similarly, Stoneley waves are interfacial waves in bonded contact of dissimilar elastic half-spaces, when the displacements are in the plane of the solids. It is shown that in slow sliding, long wavelength Love and Stoneley waves are destabilized by friction. Friction is assumed to have a positive instantaneous logarithmic dependence on slip rate and a logarithmic rate weakening behavior at steady-state. Long wavelength instabilities occur generically in sliding with rate- and state-dependent friction, even when an interfacial wave does not exist. For slip at low rates, such instabilities are quasi-static in nature, i.e., the phase velocity is negligibly small in comparison to a shear wave speed. The existence of an interfacial wave in bonded contact permits an instability to propagate with a speed of the order of a shear wave speed even in slow sliding, indicating that the quasi-static approximation is not a valid one in such problems.