Crustal structures inferred from Rayleigh-wave signatures of NTS explosions

An improved method for determining plane-layered earth models that accurately represent the important features controlling the amplitude and wave form of surface waves is presented. The method includes a formal inversion of phase and group velocity data determined from observed seismograms and is applied to the Rayleigh waves from Nevada Test Site (NTS) explosions recorded at Albuquerque, New Mexico and Tucson, Arizona. For both paths the observed dispersion agrees with that from the models with a maximum residual of only 0.01 km/sec. Further, the models are consistent with other available information about these paths (e.g., from refraction surveys). To properly account for local differences in the material at the source, an approximate theory is constructed in which the amplitude excitation is computed in a source structure and the dispersion in a separate path structure. Using this theory and the crustal models from the inversion, synthetic seismograms are computed that match the observed seismograms remarkably well.