Thesis (doctoral)--Universität Bremen, 2006. / Includes bibliographical references (p. 94-100).

Power spectral analysis using the maximum entropy method is applied to the estimation of depth to the source of magnetic anomalies. The method assumes that the source is two-dimensional and has a magnetization with random intensity. The predictive ability of the maximum entropy technique permits analysis of short segments of data in order to resolve short wavelength variations in source depth. The method does not require knowledge of susceptibilities or the magnetic declination and inclination. An application of the method to theoretical data and observed marine anomalies over the Peru-Chile trench yields encouraging results. Specifically, for the eastern margin of the Nazca plate, analyses generally indicate a continuous magnetic basement extending into the subduction zone. The basement is shallow seaward of the trench axis and deepens as the plate approaches the convergent margin. This apparent deepening is postulated to be due to the thickening of the oceanic crust and the deterioration of its magnetization, possibly caused by the compressional disruption of the basaltic layer. Landward of the trench axis, the depth estimates indicate possible uplift of the oceanic material into the lower slope of the continental margin. / Graduation date: 1976

Univ., Diss.--Bremen.

In order to quantitatively examine the crustal structure of the Panama Basin without the benefit of local seismic refraction data, the following assumptions were made: (1) No significant lateral changes in density take place below a depth of 50 km. (2) The densities of the crustal layers are those of a 50-km standard section derived by averaging the results of 11 seismic refraction stations located in normal oceanic crust 10 to 40 million years (m. y. ) in age. (3) The density of the upper mantle is constant to a depth of SO km. (4) The thickness of the oceanic layer is normal in that region of the basin undergoing active spreading, exclusive of aseismic ridges. (5) The thickness of the transition layer is 1. 1 kin everywhere in the basin. Subject to these assumptions, the following conclusions are drawn from the available gravity, bathymetry, and sediment-thickness data: (1) Structurally, the aseismic ridges are surprisingly similar, characterized by a blocky, horst-like profile, an average depth of less than 2 km, an average depth to the Mohorovicic discontinuity of 17 km, and an average free-air anomaly of greater than +20 mgal. The fact that their associated free-air anomalies increase from near zero at their seaward ends to greater than +40 mgal at their landward ends suggests that the Cocos and Carnegie ridges are uplifted at their landward ends by lithospheric bending. (2) The centers of sea-floor spreading and fracture zones are characterized by a shoaling of the bottom and an apparent deepening of the Mohorovicic discontinuity. The only exception to this generalization is the northern end of the Panama fracture zone between the Cocos and Coiba ridges. (3) The Panama fracture zone and the fracture zone at 85°20'W longitude divide the Panama Basin into three provinces of different crustal thickness. Between these two fracture zones the crustal thickness is normal; west of 85°20W longitude it is greater than normal; and east of the Panama fracture zone it is less than normal. (4) In that part of the Panama Basin east of the Panama fracture zone there is a major discontinuity at 3°N latitude between a smooth, isostatically compensated crust to the south and an extremely rugged, uplifted crust to the north. An explanation for this discontinuity is the effect of the inflection in the shape of the continental margin at 3°N latitude on the eastward subductiori of the Nazca plate. / Graduation date: 1974

The Carnegie Ridge is a linear, aseismic, submarine ridge lying between the Galapagos Islands and the coast of South America. A 2300 meter deep saddle near 86°W. longitude divides the ridge into western and eastern segments. Surface ship, near bottom, and grain size studies from the saddle have been used to delineate the present geological environment and history of the ridge. Structurally the Carnegie Ridge is rather simple in profile, being bounded by east-west trending scarps which give the ridge a block-faulted appearance. Acoustic basement over the ridge appears smooth on reflection profiles and is composed of chert. The sedimentary sequence above the chert horizon contains a lower chalk unit overlain by calcareous ooze. Where erosion has exposed the chalk a karst-like micro-topography is present which is characterized by steep walled channels and cliffs and consolidated bed forms undergoing erosion and dissolution. The ridge crest has been stripped of almost its entire sediment cover. Thick sequences of sediment are found only in areas protected from north or south flowing bottom currents. Evidence of erosion is provided by extensive channeling on both the north and south flanks of the ridge. Near bottom observations in one channel on the north flank revealed a large field of sand dunes indicating northward, downslope sediment transport. These dunes are found on a manganese-encrusted chalk which floors the channel. Hydrographic data suggest that the northward flow across the ridge may be produced by the spillover of bottom water. Near bottom and surface ship observations are consistent with a southward sediment transport on the south flank of the ridge. The mechanism responsible for this southward flow remains unresolved. Current meters deployed on the north and south flanks recorded only low speed currents, opposite in direction to the inferred sediment transport. Apparently the bottom water flow responsible for erosion and sediment transport over the ridge is episodic in nature and was not recorded during the present survey. The grain size characteristics of surface sediments respond to the same processes which control sediment distribution. Where erosion is evident over the ridge crest, coarse lag deposits of foraminiferal sand are found. Apparently the erosion is most pronounced at the sill depth on the ridge since the sediments tend to become finer both upslope and downslope from that point. Three dominant modes are present in the sand fraction from the ridge. These modes record the initial input and fragmentation of foraminiferal tests. Continued fragmentation and dissolution of these tests creates a large number of finer modes. The age of true basaltic crust over the ridge is between 10 and 26 million years. This crust was probably created during a period of very slow spreading on the Galapagos Rift Zone during the Miocene. Unconformities on the ridge indicate that erosion dates only from the mid-Pliocene. The initiation of erosion was probably in response to further uplift of the ridge. This uplift may have been related to slight southward underthrusting along the north flank of the ridge. / Graduation date: 1975 / Best scan available for figures on p.67, 96. The original is a black and white photocopy.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1983. / Grant provided by NASA under Grant NAG 6-9. Includes bibliographical references (p. 187-193).

Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 47-49). Also available by World Wide Web.

Thesis (Ph. D. in Physical Oceanography)--Naval Postgraduate School, March 2003. / Dissertation supervisor: Mary L. Batteen. Includes bibliographical references (p. 167-168). Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis--Massachusetts Institute of Technology / Woods Hole Oceanographic Institution. / Vita. Includes bibliographical references (p. 333-347).