*3.2. Model Setup*

The stress modelling is done in 2D using the state of plane stress, and carried out using the commercial software Comsol Multiphysics 5.2 and the add-on structural mechanics module. Comsol Multiphysics is a FEA (Finite Element Analysis) software, where the problem domain is divided by a mesh of triangular elements in which the calculations are done. The set-up of a stress model in Comsol Multiphysics includes defining model geometry, then adding material properties, loads and boundary conditions.

The model geometry includes faults geometries based on a published continental shelf map of Norway [45] with scale 1:2 mill, interpreted at the base of Top Jurassic. The model includes an area of approximately 300 × 300 km in the SW Barents Sea that was covered by ice during LGM. All fault geometries are manually traced in a CAD tool, and then imported into Comsol Multiphysics.

Every geometry unit of the model is assigned material properties, that is, Young's modulus and Poisson's ratio for the lithologies included. In the models presented here, the host rock is modelled as soft shale with a Young's modulus of 5 GPa and a Poisson's ratio of 0.25, which is within the typical values for shales [46]. Fault zones normally consist of numerous fractures and smaller faults which lower the general stiffness, or Young's modulus, of the host rock [47]. The faults are therefore given a Young's modulus of 0.1 GPa and Poisson's ratio of 0.25.

Next, boundary conditions are assigned to the model. As the model represents the base of a geological unit at depth, the sides of the model cannot deform freely. Two opposite boundaries of the model are therefore fixed. The other two boundaries are assigned a load representing the flexure-related extension originating from the isostatic response during the deglaciation after LGM. The orientation of the flexure-related extension is perpendicular to the curvature trends, with an orientation ~SW–NE. (Figure 6). In a study of the post-glacial lithospheric flexure in the North Sea, analytical and numerical calculation of glacial unloading (assuming isostatic equilibrium before the onset of unloading) of a 1 km thick ice sheet and a lithosphere with elastic thickness of 30 km resulted in bending stresses in the

order of 20 MPa [30]. We have used 5 MPa, which is a more conservative magnitude for this e ffect. The model does not take into consideration possible tectonic background stress at the time of glacial unloading. This modelling may therefore be considered as a study of the e ffect of stress changes due to the glacially induced flexure.
