Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 61-62). Also available via the Internet.

Thesis (Ph. D.)--University of California, San Diego, 1997. / Vita. Includes bibliographical references (leaves 230-237).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 63-65). Also available via the Internet.

"January 1992." / "Technical report." "Funding was provided by the Office of Naval Research through Contract no. N00014-91-J-1776." Includes bibliographical references (p. 7).

"January 1997." Thesis (Ph. D.)--Naval Postgraduate School, 1996. / "Prepared for: Office of Naval Research, Arlington, VA 22217-5660."

Thesis (M.Sc.)--City University of Hong Kong, 2005. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

No description available.

In this thesis, I investigate the seismic structure of oceanic lithosphere and asthenosphere with a particular focus on seismic anisotropy, using high-resolution surface waves recorded on ocean-bottom seismometers (OBS) in the Pacific and Atlantic Oceans. The NoMelt (~70 Ma) and Young OBS Research into Convecting Asthenosphere (ORCA) (~43 Ma) OBS experiments located in the central and south Pacific, respectively, provide a detailed picture of ``typical'' oceanic lithosphere and asthenosphere and offer an unprecedented opportunity to investigate the age dependence of oceanic upper mantle structure. The Eastern North American Margin Community Seismic Experiment (ENAM-CSE) OBS array located just offshore the Eastern U.S. captures the transition from continental rifting during Pangea to normal seafloor spreading, representing significantly slower spreading rates. Collectively, this work represents a diverse set of observations that improve our understanding of seafloor spreading, present-day mantle dynamics, and ocean basin evolution. At NoMelt, which represents pristine relatively unaltered oceanic mantle, we observe strong azimuthal anisotropy in the lithosphere that correlates with corner-flow induced shear during seafloor spreading. We observe perhaps the first clear Love-wave azimuthal anisotropy that, in addition to co-located Rayleigh-wave and active source Pn constraints, provides a novel in-situ estimate of the complete elastic tensor of the oceanic lithosphere. Comparing this observed anisotropy to a database of laboratory and naturally deformed olivine samples from the literature leads us to infer an alternative ``D-type'' fabric associated with grain-size sensitive deformation, rather than the commonly assumed A-type fabric. This has vast implications for our understanding of grain-scale deformation active at mid-ocean ridges and subsequent thermo-rheological evolution of the lithosphere. At both NoMelt and YoungORCA we observe radial anisotropy in the lithosphere with Vsh > Vsv indicating subhorizontal fabric, in contrast to some recent global models. We also observe azimuthal anisotropy in the lithosphere that parallels the fossil-spreading direction. Estimates of radial anisotropy in the crust at both locations are the first of their kind and suggest horizontal layering and/or shearing associated with the crustal accretion process. Both experiments show asthenospheric anisotropy that is significantly rotated from current-day absolute plate motion as well as rotated from one another, at odds with the typical expectation of plate-induced shearing. This observation is consistent with small-scale density- or pressure-driven convection beneath the Pacific basin that varies in orientation over a length scale of at most ~2000 km and likely shorter. By directly comparing shear velocities at YoungORCA and NoMelt, we show that the half-space cooling model can account for most (~75%) of the sublithospheric velocity difference between the two location when anelastic effects are accounted for. The unaccounted for ~25% velocity reduction at YoungORCA is consistent with lithospheric reheating, perhaps related to upwelling of hot mantle from small-scale convection or its proximity to the Marquesas hotspot. While lithospheric anisotropy is parallel to the fossil-seafloor-spreading direction at both fast-spreading Pacific locations, it is perpendicular to spreading at the ENAM-CSE in the northwest Atlantic where spreading was ultra-slow to slow. Instead, anisotropy correlates with paleo absolute plate motion at the time of Pangea rifting ~180–195 Ma. We propose that ultra-slow-spreading environments, such as the early Atlantic, primarily record plate-motion modified fabric in the lithosphere rather than typical seafloor spreading fabric. Furthermore, slow shear velocities in the lithosphere may indicate that normal seafloor spreading did not initiate until ~170 Ma, 10–25 Myr after the initiation of continental rifting, revising previous estimates. Alternatively, it may shed new light on melt extraction at ultra-slow spreading environments.

Lifelines such as highways, pipelines, telecommunication lines, and powerlines provide communities with vital services, and their functionality is dependent upon the foundation soil that supports them. However, when designing the infrastructure, it can be difficult to know where to test the soil in order to give spatially representative sampling, particularly for long, lifeline structures. Finding this distance requires knowledge of the spatial correlation and/or the spatial variability of the soil parameter (stiffness, cohesion, etc.). But this correlation distance is not typically found in practice because it requires large amounts of data and the costs of retrieving that data can be high. Lack of representative sampling can lead to an overly conservative design and too much sampling can create an overly expensive sampling program. In this study, multiple tests using the geophysical method of spatial autocorrelation (SPAC) were conducted to find the soil stiffness along a 310 meter long profile. SPAC records passive surface waves which sample the underlying soil, and these surface waves can be used to create a shear wave velocity profile of the site. The spatial continuity of the stiffness (the soil velocity values) was then found using geostatistics. The geostastical tool primarily used in this study was the (semi-)variogram, but the covariance function and the correlogram are also shown. By using these tools, the spatial correlation/variability can give an estimate of the how far apart to test the foundation soil so that the data is spatially representative. In other words, finding the distance that the soil parameter is minimally correlated with itself. This study found the distance (the range of the semi-variogram) to be 70 meters for 5 meters depth, 100 meters for 10 to 15 meters depth, and 90 meters for 30 meters depth.

No description available.