Investigating the Bias in GPS-derived 1-D Viscosity Models due to Antarctica's Complex 3-D Mantle Structure

The viscoelastic Earth structure beneath the Antarctic ice sheet is an important control on future ice sheet dynamics and a key factor in sea-level reconstructions. While seismic studies indicate that three-dimensional mantle structure beneath Antarctica is complex, and includes a low (10¹⁸-10¹⁹ Pa s) viscosity upper mantle in the West, the conversion from seismic wave speed to viscosity is highly uncertain. This complexity has been avoided in recent analyses of GPS data which, in tandem with forward models of crustal deformation due to glacial isostatic adjustment (GIA), have inferred 1-D viscoelastic structure beneath the West Antarctic.

We investigate what these 1-D viscosity models represent in a region with complex 3-D mantle structure, and over what geographic length-scale they might be applicable. To do so, we first generate synthetic observations of present-day, 3-D crustal deformation rates using 3-D viscoelastic Earth structure inferred from seismic tomography and a finite volume treatment of GIA, and compare these rates with a suite of 1-D forward Earth model predictions. With this insight, we turn to an analysis of available GPS sites and consider their depth and lateral sensitivity to 3-D mantle viscosity structure.