Linear or nonlinear rheology in the mantle: a 3D finite-element approach to postglacial rebound modeling

In a previous work, cast in axisymmetric flat geometry, we have shown that a realistic composite rheology (linear plus nonlinear) for the Earth's mantle reproduces the postglacial isostatic readjustment of Laurentia significantly better than a purely linear one. In this work we address the same problem in a 3D flat geometry allowing to apply the ice load described by the ICE-3G deglaciation history without manipulations. Computation is numerically carried out through finite elements as the nonlinear formulation prevents the use of spectral methods. The goodness of fit is quantitatively tested by comparing observed and computed Relative Sea Level (RSL) data at 29 North American sites for the last 8 kyr. The mixed rheology model still shows a slightly but significantly better fit (in the statistical sense) than the linear model.