| Recent high-resolution global models of lateral variations in surface-wave velocities contradict each other. While the models parameterize structures as small as 500 km, they are consistent only for wavelengths longer than 4000 km. This disagreement causes confusion and frustration on the part of Earth scientists who try to make use of the models. This thesis addresses this ambiguity in surface-wave velocities by trying to understand better the sources of uncertainty and by developing new ways to better constrain the models. The thesis studies both Love and Rayleigh waves in the period range 35 s to 175 s, which are sensitive to seismic velocities from the crust to the transition zone.; In order to better compare global models with regional models, I derive measurements of group velocity from phase-velocity dispersion curves and model them with global laterally-varying isotropic structure. For the area of Eurasia, the new maps are in very good agreement with a recent regional study, particularly in terms of spatial correlation.; Existing models do not take into account the effects of azimuthal anisotropy. I derive practical dynamical ray tracing equations for anisotropic phase-velocity maps and, using perturbation theory, I obtain approximate expressions for surface-wave observables. I present hypothetical examples to simulate isotropic modeling of surface waves which pass through anisotropic material. The experiment shows that the effects of anisotropy are mapped into short wavelength isotropic structure.; Arrival-angle data is more sensitive than phase data to structures of intermediate scale length. I develop a new, fully automated method for measuring surface-wave arrival angles. The method is accurate to between 1.5° and 3°, depending on wavetype and frequency. I apply the technique to a large database of surface-wave seismograms. The measurements allow for the determination of misorientations of seismometers and the evaluation of existing phase-velocity models.; New models of global phase-velocity are created including the arrival-angle data measured with the new method. Major-arc and minor-arc phase data are also included in the modeling to constrain long-wavelength structures. The models provide improved fits to the data, appear physically reasonable, and compare favorably to existing models of phase velocity.*; *Dissertation includes a CD-ROM. |
