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Data collected by personnel of the Geophysics Group at Oregon State University and the Instituto Oceanografico of the Direccion General dé Oceanografia are used to construct a free-air anomaly map for the central part of the Pacific continental margin of Mexico, which shows the gravity expression of major structural features in the region. Specific features are the Middle America and Rivera trenches intersected by a possible extension of the Rivera Fracture Zone, and the Ulloa Trough on the western side of Baja California. Of particular importance are gravimetric minimums with no bathymetric expression observed east of the Tres Marias Islands, southeast and northwest of the Tamayo Fracture Zone, and as extensions of the bathymetrically mapped series of en echelon faults within the Gulf of California. A geophysical model cross section constructed along a profile southeast of the Tres Marias Islands indicates a continental type crust east of the islands with a Moho depth of 13 km at the base of the Tres Marias Scarp and dipping toward the continent. The structure at the transition zone between oceanic and continental crust suggests active subduction of the oceanic crust in the past followed by a period of shear or strike-slip motion. The thickness of the sediments along the cross section and east of the Tres Marias Islands reaches 1.5 km. / Graduation date: 1981

Gravity, magnetic and seismic data indicate that the oceanic crust is 9.7 km thick west of the Continental Borderland. The top of the mantle is about 12 km deep under the Borderland, and deepens to 27 km beneath the Peninsular Ranges of Baja California. The mantle is about 20 km below the surface of the Imperial Valley and deepens to 27 km under the area east of the Imperial Valley. The age of the youngest detectable remnant magnetic anomaly over the oceanic crust is about 16.5 million years at 21.3°N Lat. and decreases to the south. A magnetic anomaly expected along the continuation of the San Benito Fault Zone is not detected by this study. A gravity low along the base of the Patton Escarpment is at least partially the result of a buried trench-like depression. In the vicinity of 31.3°N Lat., 119.3°W Long. this depression is filled with 2 km of sediments. The geophysical and geological data are interpreted as indicating a 6 km thick section of Franciscan rocks that extends from the west edge of the Borderland to the Coronado Escarpment. Magnetic data suggest that an ophiolite may be present within or on top of the Franciscan rocks. Several of the ridges in the Borderland have cores of high density rocks which are interpreted as intrusives. The area just south of the San Clemente basin has an anomalously thin upper crust. The gross crustal structure of this region is comparable to the Imperial Valley region and may represent a former site of crustal rifting which occurred when the East Pacific Rise was subducted under this part of the North American plate. North of the Santo Tomas Fault Zone are several basins filled with more than 3 km of sediments, but south of this fault zone the sediment cover is discontinuous and generally less than 2 km thick. / Graduation date: 1978

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 117-134).

Graduation date: 1981

Thesis (PhD)--University of South Australia, 2001.

Thesis (doctoral)--Friedrich-Wilhelm-Universität Bonn.

Thesis (doctorat d'etat ès sciences naturelles)--Université Pierre et Marie Curie, Paris, 1976. / "No d'enregistrement au C.N.R.S., 12.305." Includes bibliographical references (p. 117-137).

Dyke injection transports large volumes of magma over great distances, controlling the supply of magma to volcanoes and effectively releasing tensional stress at divergent plate margins. This thesis aims to improve understanding of dyke injection processes on different scales. Dyke shapes measured on the Isle of Rum have been analysed and show a mismatch between the currently accepted theory used to describe their shape, and the measured data. The measured dykes show wider edges than expected, consistent with wedging and cooling of magma in the dyke tips; wedged dykes can act as conduits for longer. Finite difference one- and two-dimensional models for the thermal evolution of the crust due to heat transfer from multiple dyke injection have been developed and applied to the geological setting of the actively spreading Main Ethiopian and Red Sea rifts, where the spreading rates are 5 and 16 mm yr-1 respectively. The model has shown that the spreading rate is the first order control on the temperature build up. Differences in crustal thickness exist between these two regions; the crust has thinned under the Red Sea Rift whilst under the Main Ethiopian Rift there has been no appreciable thinning. This difference has led to the conclusion that the spreading rate, and thus the temperature profile, is the principal cause for the differences in crustal thicknesses. Above the brittle-ductile transition temperature, the crust is likely to undergo pre- dominantly ductile deformation; for slow spreading rates (e.g. 5 mm yr-1), it takes up to 142 ka for the dyke injection site to reach this temperature. The position of the locus of strain at an actively rifting margin migrates with time. For slow spreading rates, the strain locus must remain fixed for at least 142 ka before appreciable crustal heating allows the onset of ductile stretching. Where the spreading rate is faster, the locus of strain must remain fixed for shorter lengths of time. Thus Ethiopia's evolving locus of strain and low spreading rate have likely caused much of the extension to be accommodated by magmatic intrusion rather than by stretching. Comparisons between the thermal model results and geophysical observations from a segment of the Red Sea rift have been made. The mag- netotelluric survey across the rift axis of the actively spreading Red Sea Rift segment has shown two bodies of hot material; one explanation is that the rift axis has jumped. Scaled experimental models have been used to study multiple dyke injection in an extensional tectonic setting. For a fixed overpressure, larger spacings between injections give smaller rotation angles between injections. This is consistent with the rotation angles and injection spacings observed between the recent dyke injections on the Red Sea Rift.

Soybean (Glycine max (L.) Merr.) are one of Mississippi’s most profitable agricultural crops. White-tailed deer (Odocoileus virginiaus) damage soybean every year due to the plant’s high palatability, digestibility and nutritional content. I estimated the amount of damage (browsing and loss of yield) caused by deer within 5 soybean fields in eastern Mississippi and compared damage to the number of deer using each field during the 2012 and 2013 growing seasons. I assessed the effectiveness of the chemical repellent Hinder on soybean. While deer did affect soybean height, soybean yield remained unaffected during both years of my study. Given the results of this study, the perception of deer damage may be greater than the physical damage and other environmental factors such as field margin effects may be the reason for spatial variations in soybean yield throughout fields. Hinder also improved soybean height and decreased deer damage but soybean yield remained unchanged.