Combined Receiver-Function and Surface Wave Phase-Velocity Inversion Using a Niching Genetic Algorithm: Application to Patagonia

A combined inversion of body wave receiver functions and Rayleigh wave phase velocities using a niching genetic algorithm (NGA) increases the uniqueness of the solution over separate inversions and also facilitates explicit parameterization of layer thickness in the model space. This parameterization requires fewer layers and a priori constraints for modeling more complex structures than traditional linearized inversion. NGAs solve for a suite of locally optimal solutions in addition to isolating the globally optimal solution by using an evolutionary paradigm. This nonlinear examination of the error space provides an opportunity to examine trade-off within the model space. The method, when applied to synthetic data, locates interfaces within 2 km of the test structure and identifies appropriate structure and velocity. Applying this method to data from a deployment of five broadband stations in Chilean Patagonia yields a regional model of crustal structure that is consistent with the geological history of the region. Sediment thickness is inversely proportional to crustal thickness, with sediment thicknesses reaching more than 4 km, where the crustal thickness thins to 28 km. This is consistent with previous geological studies, which suggests that the Rocas Verdes basin in western Patagonia formed by crustal thinning, isostatic compensation, and subsequent sedimentation.