No abstract

No abstract

A variety of geologic observations point to fast upper mantle flow that may exceed plate tectonic velocities by an order of magnitude. At the same time there is mounting evidence from seismology for flow-like structures in the upper 100-200 km of the mantle. Here we present a set of geodynamic simulations to link these observations. In a synthetic setting, we include asthenospheric channels of varying thickness, with an extreme case of 100 km, and a significant viscosity contrast of up to 4 orders of magnitude relative to the deeper mantle. Using our new global high-resolution code TERRA-NEO, we obtain an increase in velocity by a factor of 10 between a 1000 km thick and the very thin channel, translating into velocities of ∼20 cm/a within the narrow asthenosphere. We further present and verify a simple Poiseuille flow model, predicting that the upper mantle velocity scales with the inverse of the asthenosphere thickness.

We propose a modified local discontinuous Galerkin (LDG) method for second-order elliptic problems that does not require extrinsic penalization to ensure stability. Stability is instead achieved by showing a discrete Poincaré-Friedrichs inequality for the discrete gradient that employs a lifting of the jumps with one polynomial degree higher than the scalar approximation space. Our analysis covers rather general simplicial meshes with the possibility of hanging nodes.

No abstract