Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 87-88).

Thesis (Ph. D.)--University of Washington, 1991. / Vita. Includes bibliographical references (leaves [133]-153).

Graduation date: 1994

Bibliography: leaves 238-257. / ix, 257 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Develops a tomographic seismic inversion scheme that makes use of first arrivals and later arrivals simultaneously ; is easier to analyse in terms of convergence, stability and uniqueness of solutions; and is a proper non-linear inversion scheme. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 1998?

Thesis (Ph. D.)--California Institute of Technology, 1985. / Typescript (photocopy). Includes bibliographical references (leaves 183-189).

Thesis (Ph. D.)--California Institute of Technology, 1984. / Includes bibliographical references (leaves 213-230).

The computation of traveltimes plays a critical role in the conventional implementations of Kirchhoff migration. Finite-difference-based methods are considered one of the most effective approaches for traveltime calculations and are therefore widely used. However, these eikonal solvers are mainly used to obtain early-arrival traveltime. Ray tracing can be used to pick later traveltime branches, besides the early arrivals, which may lead to an improvement in velocity estimation or in seismic imaging. In this thesis, I improved the accuracy of the solution of the linearized eikonal equation by constructing a linear system of equations (LSE) based on finite-difference approximation, which is of second-order accuracy. The ill-conditioned LSE is initially regularized and subsequently solved to calculate the traveltime update. Numerical tests proved that this method is as accurate as the second-order eikonal solver. Later arrivals are picked using ray tracing. These traveltimes are binned to the nearest node on a regular grid and empty nodes are estimated by interpolating the known values. The resulting traveltime field is used as an input to the linearized eikonal algorithm, which improves the accuracy of the interpolated nodes and yields a local ray-based traveltime. This is a preliminary study and further investigation is required to test the efficiency and the convergence of the solutions.

Wavefield extrapolation in orthorhombic anisotropic media incorporates complicated but realistic models, to reproduce wave propagation phenomena in the Earth's subsurface. Compared with the representations used for simpler symmetries, such as transversely isotropic or isotropic, orthorhombic models require an extended and more elaborated formulation that also involves more expensive computational processes. The acoustic assumption yields more efficient description of the orthorhombic wave equation that also provides a simplified representation for the orthorhombic dispersion relation. However, such representation is hampered by the sixth-order nature of the acoustic wave equation, as it also encompasses the contribution of shear waves. To reduce the computational cost of wavefield extrapolation in such media, I generate effective isotropic inhomogeneous models that are capable of reproducing the first-arrival kinematic aspects of the orthorhombic wavefield. First, in order to compute traveltimes in vertical orthorhombic media, I develop a stable, efficient and accurate algorithm based on the fast marching method. The derived orthorhombic acoustic dispersion relation, unlike the isotropic or transversely isotropic one, is represented by a sixth order polynomial equation that includes the fastest solution corresponding to outgoing P-waves in acoustic media. The effective velocity models are then computed by evaluating the traveltime gradients of the orthorhombic traveltime solution, which is done by explicitly solving the isotropic eikonal equation for the corresponding inhomogeneous isotropic velocity field. The inverted effective velocity fields are source dependent and produce equivalent first-arrival kinematic descriptions of wave propagation in orthorhombic media. I extrapolate wavefields in these isotropic effective velocity models using the more efficient isotropic operator, and the results compare well, especially kinematically, with those obtained from the more expensive anisotropic extrapolator.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 100-103. Also available online.

Thesis (M.S.)--University of Toledo, 2007. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science in Geology." "A thesis entitled"--at head of title. Accompanied by CD-ROM which contains the following files: 2000-2003 Teleseismic Reduced Traveltimes.xls; 2000-2003 Teleseismic Traveltimes.xls; 2004 Teleseismic Reduced Traveltimes.xls; 2004 Teleseismic Traveltimes.xls; 2005 Teleseismic reduced Traveltimes.xls; 2005 Teleseismic Traveltimes, xls; 2006 Teleseismic Reduced Traveltimes. xls; 2006 Teleseismic Traveltimes. xls; Complete Thesis.doc; Regional Earthquake Data.xls; Teleseismic Earthquake Data.xls. Bibliography: leaves 78-80.