The Importance of the Inelastic and Elastic Structures of the Crust in Constraining Glacial Density, Mass Change, and Isostatic Adjustment From Geodetic Observations in Southeast Alaska

Elastic deformation of the solid Earth in response to ice mass loss offers a promising constraint on the density of glacial material lost. Further, the elastic response to modern deglaciation is important to constrain for studies of glacial isostatic adjustment to determine the mantle's structure and rheology. Models of this elastic uplift are commonly based on the 1-D, seismically derived global average Preliminary Reference Earth Model and typically neglect uncertainties that can arise from regional differences in elastic structure from that of the global average, lateral heterogeneities within the region, and inelastic behavior of the crust. We quantify these uncertainties using an ensemble of 1-D local elastic structure models and empirical relations for the effects of inelasticity in the upper approximate to 10km of the crust. In Southeast Alaska, modeling elastic uplift rates with local elastic structures results in up to a 20-40% difference from those modeled with the Preliminary Reference Earth Model. Although these differences are limited to regions near to ice-covered areas, they are comparable to the differences in uplift rates expected from the loss of firn versus loss of ice. Far from ice-covered areas, where most of the region's GPS observations were made, these differences become insignificant and do not affect previous glacial isostatic adjustment studies in the region. The methods presented here are based on the globally available LITHO1.0 seismic model and open source software, and the approach of using an ensemble of 1-D elastic structures can be easily adapted to other regions around the world.