Abstract
A Newton method is presented for the approximate solution of the inverse problem to determine the shape of a two-dimensional crack from a knowledge of the far field pattern for the scattering of time-harmonic elastic plane waves. Fréchet differentiability with respect to the boundary is shown for the far field operator, which for a fixed incident wave maps the crack onto the far field pattern of the scattered wave. Some numerical reconstructions illustrate the feasibility of the method.