Assessing the influence of geometrically non-linear effects on earthquake fault plane inversions. G.J. van Zwieten, M.A. Gutierrez and R.F. Hanssen To deduce from coseismic surface displacement the exact source parameters of an earthquake through inversion, one needs a forward model that predicts displacements for given fault geometry and slip. Often used for this purpose are the analytical solutions by Okada for constant dislocations in an elastic half space, thereby assuming that the earth behaves approximately elastically over short time scales. Although the Okada solutions solve the governing differential equations exactly, they do have a potential flaw. That is: the assumption of geometric linearity that lies at the basis of these equations is valid everywhere in the solid except at the discontinuous displacement jump that is formed by the fault. A large jump will lead to a non-physical discontinuity in the computed stress field. This contribution presents a study of this potential problem. Using finite element code written specially to enforce continuity of stress everywhere in the domain is possible to compare the results of linear and non-linear computations. The main question that will be answered is what can be gained by using a forward model in fault plane inversions that correctly deals with non-linearity.