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Constrained Parameterization of the Multichannel Analysis of Surface Waves Approach with Application at Yuma Proving Ground, Arizona
Schwenk, Jacob Tyler
Schwenk, Jacob Tyler
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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.
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Date
2013-08-31
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University of Kansas
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Keywords
Geophysics, Geology, Inversion, Masw, Rayleigh wave, Refraction, Surface wave, Swm