Many problems to be solved in geophysical processing can be expressed in terms of identiication of spatial geological models : given a function F applied to a geological model G, producing a result R, the problem is to find G such that F(G) = R* , where R* is the expected result : a seismogram, a pressure curve, a seismic cross-section etc. The presented research deals with the joint use of evolutionary algorithms and Voronoi diagrams to address some non-parametric instances of identification problems in geophysics, i.e. without a priori hypothesis about the geometrical layout of possible solutions. In this paper, a first application in velocity determination for seismic imaging demonstrates the ability of this approach to identify both the geometry and the velocities of the underground from experimental seismograms.