Pore Pressure Changes Driven Seismic and Aseismic Basal Slip in Glacier Ice Sheets

Abstract

This study considers the development of basal slip in glacier ice sheets. We consider a simple mechanical model of the glacier ice sheet where a thin deformable thin slab of ice undergoes differential slip at the base. The thin layer deforms in an elastic manner and the friction at the base is considered to be slip-rate and state-dependent. Here we study how a local source of pore water pressure at the base of the glacier could initiate a rapid seismic slip or slow aseismic creep. We explore how pre-pressure diffuses along the glacier base can lead to reduced frictional strength of the interface; and in turn, promotes slip at the base. The model considers three physical processes to simulate the dynamics of the basal slip: (i) elastic deformation of the thin slab of the glacier, (ii) slip rate, and history-dependent (iii) pore-pressure diffusion along the base of the thin slab. We find that the pre-pressure source can alone re-activate slip without any external driving stress. The pre-stress along the fault and pore pressure both dictate the development of slip. The combination of these three physical processes leads to a system of three partial differential equations that govern the evolution of the slip rate, slip state, and pore pressure along the base of the glacier. We numerically solve the coupled partial differential equations method of lines. To calculate the derivatives, we use MATLAB’s FFT subroutine. We find that pore pressure diffusion can lead to rapid slip when basal frictional properties are rate-weakening. The pore-pressure diffusion can lead to slow aseismic creep when basal frictional properties are rate-strengthening. We find that the coupled PDEs governing slip rate evolution ae numerically stiff. For rate-strengthening case, we use similarity solution for pore pressure diffusion and numerical solution for slip rate and state evolution. We find that creep propagation significantly outpaces the pore pressure diffusion regime.