Impact of elastic structure variations on constraints of glacial density and GIA in southeast Alaska

Elastic deformation of the solid Earth in response to ice mass loss offers a promising constraint on the density of lost glacial material, which can be difficult to measure directly. Further, the elastic response to modern deglaciation is important to constrain in studies of Glacial Isostatic Adjustment (GIA) to determine the mantle's structure and rheology. A common approach for both glaciological and GIA studies is to model the elastic deformation using estimates of ice mass balance and a radially symmetric Earth model described by the seismically derived 1D global average Preliminary Reference Earth Model (PREM). Uncertainties due to the choice in elastic structure have largely been neglected but could directly impact both GIA and glaciological studies. The mountainous and often volcanic settings of most glaciated regions have heterogeneous crust that may not be well described by PREM, and anelastic interactions with pores and fractures in the crust during ice unloading are not captured by seismically derived elastic structures. This study quantifies the impact of these uncertainties on previous GIA studies in southeast Alaska and on glaciological studies constrained by elastic deformation using an ensemble of LITHO1.0 1D seismic velocity models and empirical relations for the effects of anelasticity. Elastic uplift rates estimated using the LITHO1.0 ensemble are up to 75-150% different than those estimated using PREM, comparable to the density contrast between firn and ice. At distances beyond 2.5km from ice covered areas, where most of the region's GPS observations were made, these differences become insignificant and do not affect previous GIA studies in the region. We present preliminary results of interferometric synthetic aperture radar (InSAR) based estimates of deformation in regions where the elastic uplift is most sensitive to the elastic structure of the crust. In-situ estimates of crustal elastic structure are compared to the LITHO1.0 ensemble and empirical anelasticity relations. Conversely, using the LITHO1.0 elastic structure ensemble and observed deformation we explore the limits of using elastic deformation for constraining the mass and density of glacial material lost.