Lateral viscosity variations beneath Antarctica and their implications on regional rebound motions and seismotectonics

Abstract

Abstract The Antarctic Ice Sheet has experienced large ice volume changes during the late Pleistocene glacial cycles. However, the exact amount and areas of mass change are difficult to establish, as both glaciological reconstructions and climate models rely on relatively sparse data sets, when compared to Northern Hemisphere data. We assess the potential contributions to present-day crustal motions and seismicity from glacially-induced ice mass changes. Three different scenarios for the late-Pleistocene ice-sheet distributions are considered. The viscoelastic response of the bedrock is computed for two earth models, a model with radially varying mantle viscosity only, and a model with three-dimensional viscosity variations based on a recent seismic tomographical study. In the latter model, East Antarctica is underlain by a stiff cratonic root, while the upper mantle underneath West Antarctica is weak. Our predicted present-day crustal motions depend strongly on the ice model chosen, with vertical motions focused on areas of former late Pleistocene ice domes. The horizontal motions are greatly affected by the earth rheology, as the horizontal flow pattern is controlled by the flow from the stiff East Antarctic cratonic root to the weaker West Antarctic mantle. Glacially-induced changes in fault stability margin are positive over much of Antarctica, indicating a seismically quiet state due to the large present-day ice sheet. At the site of the 1998 Balleny Island Earthquake ( M w = 8.1 ), the stresses are relatively small by comparison, and interestingly become more prone to stress failure, when a three-dimensional earth model is assumed.