Inversion of Seismic Surface Wave Data to Resolve Complex Profiles

For a complex layered site, development of a shear wave velocity profile from inversion of seismic surface wave data can yield nonunique results. One class of solutions provides depth-averaged profiles that are useful but do not detail the local velocity anomalies. Simulated annealing inversion can be used to establish whether nonuniqueness is a concern for a particular case and, if so, focus results to allow a solution that is expected based on independent knowledge of site conditions. A two-step process is recommended whereby the model parameters are first optimized using simulated annealing and then fine tuned by unconstrained linearized inversion. The process also yields useful confidence measures. One example of a complex layered site where the proposed procedure is helpful is a desert profile with high-velocity cemented layers interspersed among uncemented sediments.