Effect of Uncertainty in Viscosity Maps from Seismology on GIA Modelling

Abstract:

3D variations in viscosity have a significant effect on predictions of Glacial Isostatic Adjustment (GIA) models, such as uplift and gravity rate, which are used in a wide range of applications. 3D viscosity maps can be derived from global seismic tomography models. However, the conversion of seismic velocities to mantle temperature and viscosity is subject to large uncertainties due to unknown mantle composition and anelastic corrections (the correction for dispersion of seismic velocities due to anelastic effects). Also the seismic velocities themselves have large uncertainties. Here we investigate these uncertainties and their effect on GIA model predictions.

The largest variations in temperature between different tomography models (up to 200 K) occur in the regions of the mantle with the lowest temperatures, because the anelastic correction reduces temperature sensitivity for high temperatures. The effect of different assumptions for mantle composition in the conversion of seismic velocity anomalies to mantle temperature leads to variations in mantle temperature of 30-40K. Preliminary results from employing viscosity maps from two different tomography models in a GIA model show variations in predicted present-day uplift rates of several mm/year.