Seminar

Most models of Glacial Isostatic Adjustment (GIA) assume that the Earth is laterally homogeneous. However, seismic and geological observations clearly show that the Earth’s mantle is laterally heterogeneous. Previous studies of GIA with lateral heterogeneity mostly focused on its effect or sensitivity on GIA predications, and it is not clear to what extent can lateral heterogeneity solve the misfits between GIA predictions and observations. Our aim is to search for the best laterally heterogeneous GIA models that can simultaneously fit the global relative sea-level (RSL) data, the peak uplift rates (u-dot from GNSS) and peak gravity-rate-of-change (g-dot from the GRACE satellite mission) in Laurentia and Fennoscandia. 

A Coupled Laplace-Finite Element Method is used to compute gravitationally self-consistent sea level change with time dependent coastlines and rotational feedback in addition to changes in deformation, gravity and the state of stress. 

Fixed with the ICE-6G_C ice history model and Bunge & Grand’s seismic tomography model, started from the background viscosity models that close to VM5a. Several laterally heterogeneous mantle viscosity models are found to fit the global RSL data better than laterally homogeneous models. Two of these laterally heterogeneous mantle viscosity models also fit the peak g-dot and u-dot rates observed in Laurentia simultaneously. However, no model that is able to fit the present-day g-dot and u-dot data in Fennoscandia has been found. Then the effects of laterally heterogeneous lithosphere, sub-lithospheric and asthenospheric properties are studied and we confirm that they can affect the predicted global RSL, present-day g-dot and u-dot in Laurentia and Fennoscandia significantly. Next, we allow the heterogeneity under Fennoscandia to be different from that under Laurentia and show that this can help to further improve the fit to the observed data. Also the sensitivity of our results to different ice history model, seismic tomography model and background viscosity profile are investigated. Finally, we confirm that the ice history of ICE-6G_C in Fennoscandia and Barents Sea needs some modifications.