Constrained Parameterization of the Multichannel Analysis of Surface Waves Approach with Application at Yuma Proving Ground, Arizona

Abstract

Field data from Yuma Proving Ground, Arizona was used to test the feasibility of merging common multichannel analysis of surface waves (MASW) processing routines with mode- consistent shear-wave refraction traveltime tomography and synthetic modeling to optimize and constrain inversion results. Shear-wave first-arrival refraction tomography was used to enhance layer-model resolution and refine the MASW layer model with independent body-wave information. Shear-wave tomograms suggested a high-velocity layer, not found in initial `smooth' MASW velocity sections that were used as initial models for tomographic inversion. Increasing the stratification of the MASW layer model, to generally match tomogram structure, resulted in a higher-resolution MASW model constrained through joint analysis. This mutual analysis of shear-wave velocity (Vs) provided multiplicity to the structural interpretation of the site. Constrained-parameterization MASW results, compressional-wave tomography (Vp:Vs ratio), and density well logs populated a 2D model for numerical modeling, which was manually updated over several iterations to converge upon the site's first-arrival and dispersion characteristics. Further evaluation of the synthetic seismograms gave insight into the relationship between acquisition geometry (offset selection) and the associated dispersion-image character. Furthermore, modeling gave a secondary measurement on depth to half-space, velocity structure, and relative Vp:Vs ratios, which formulated a final MASW profile. The gradual change of the earth model, given an evolving hierarchy of constraint, is seen as the main finding of this thesis. The calculated movement towards a higher-resolution inversion based on joint geophysical measurements, analysis, and interpretation, engenders a constrained-parameterization solution with highest confidence.