Earthquake Sequence Dynamics at the Interface Between an Elastic Layer
and Underlying Half-Space in Antiplane Shear
Abstract
We quantify sliding stability and rupture styles for a horizontal
interface between an elastic layer and stiffer elastic half-space with a
free surface on top and rate-and-state friction on the interface. This
geometry includes shallowly dipping subduction zones, landslides, and
ice streams. Specific motivation comes from quasi-periodic slow slip
events on the Whillans Ice Plain in West Antarctica. We quantify the
influence of layer thickness on sliding stability, specifically whether
steady loading of the system produces steady sliding or sequences of
stick-slip events. We do this using both linear stability analysis and
nonlinear earthquake sequence simulations. We restrict our attention to
the 2D antiplane shear problem, but anticipate that our findings
generalize to the more complex 2D in-plane and 3D problems. Steady
sliding with velocity-weakening rate-and-state friction is linearly
unstable to Fourier mode perturbations having wavelengths greater than a
critical wavelength (λ_c). We quantify the dependence of λ_c on the
rate-and-state friction parameters, elastic properties, loading, and the
layer thickness (Η). We find that λ_c is proportional to sqrt(Η) for
small Η and independent of Η for large Η. The linear stability analysis
provides insight into nonlinear earthquake sequence dynamics of a
nominally velocity-strengthening interface containing a
velocity-weakening region of width W. Sequence simulations reveal a
transition from steady sliding at small W to stick-slip events when W
exceeds a critical width (W_cr), with W_cr proportional to sqrt(H) for
small H. Overall this study demonstrates that the reduced stiffness of
thin layers promotes instability, with implications for sliding dynamics
in thin layer geometries.