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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Marine geophysical studies of the southern margins of the Iberian Peninsula

Chaudhury, Suman January 1999 (has links)
A wide variety of tectonic settings are juxtaposed at the southern margins of the Iberian Peninsula. The regional geology comprises an Atlantic passive margin in western Iberia, the convergent eastern part of the Azores-Gibraltar plate boundary zone between Africa and Eurasia, and an orogenic arc (the Betic-Rif mountains) surrounding an extensional basin (the Alboran Sea). The complex tectonic history of the southern Iberian margins is recorded in its sediments and structure, and these were investigated in this study using multichannel seismic reflection techniques in conjunction with other marine geophysical data. Multichannel seismic reflection and well data from the Gulf of Cadiz have shown that the earliest sediments are Triassic evaporites, followed by Jurassic carbonates, which form rotated fault blocks in the Gulf of Cadiz. Backstripping and thermal modelling has indicated that a rifting event took place in the Late Jurassic, which stretched the crust by ~20-50%. Gravity modelling, and mapping of stretching factors, has suggested that two zones of thinning underlie the Gulf of Cadiz, which are related to the original rifting event. Backstripped subsidence curves indicate passive margin thermal subsidence until the Miocene, when westward-directed thrusting and loading from the Betic-Rif mountain belt is reflected in a typical foreland basin tectonic subsidence signature of accelerated subsidence with time. A giant, chaotic body of allochthonous sediment was emplaced into the central Gulf of Cadiz as westward migration of the Gibraltar Arc led to oversteepening of the margin west of the Gibraltar Straits, while the Alboran Sea was simultaneously undergoing active extension. These allochthonous deposits are composed mainly of Triassic evaporites and Palaeogene shales. In the Gulf of Cadiz and Seine Abyssal Plains this body has the appearance of an accretionary wedge, but a 300 km long northern lobe of the body extends into the Horseshoe Abyssal Plain. This lobe is interpreted as being a cumulative mass wasting feature, formed by the gravity-driven downslope transport of large allochthonous masses as debris flows and slides and slumps, encouraged by a regional gradient and a pre-existing trough in the Horseshoe Abyssal Plain. The total volume of sediments involved was of the order of 72 000 km 3 , and the time of emplacement has been estimated as being Tortonian on the basis of seismic correlation with core data at DSDP site 135. This chaotic unit has formed a series of longitudinal diapiric ridges in the northern Gulf of Cadiz, which have been interpreted to act as a transport system for gas generated in the lower slope area to migrate to the upper slope where gas-related features are seen. Gas hydrates are present beneath the lower continental slope, as inferred from a bottom-simulating reflection on seismic reflection profiles.
32

Structural interpretation of seismic reflection data from the eastern Salt Range and Potwar Plateau, Pakistan /

Pennock, Edward S. January 1988 (has links)
Thesis (M.S.)--Oregon State University, 1988. / Typescript (photocopy). Includes bibliographical references (leaves 69-78). Also available on the World Wide Web.
33

Common conversion point stacking for P-SV converted waves /

Zhang, Yaohui. January 1992 (has links)
Thesis (Ph.D.)--University of Tulsa, 1992. / Bibliography: leaves 123-131.
34

An investigation of constant velocity gradient effects in seismic analysis /

Dahanayake, Bandula Wickramaratna, January 1983 (has links)
Thesis (M.Eng.) -- Memorial University of Newfoundland, 1984. / Bibliography : leaves 91-92. Also available online.
35

Seismic refraction and reflection in the Caribbean Sea

Edgar, Norman Terence, January 1968 (has links)
Thesis (Ph. D.)--Columbia University, 1968. / Includes bibliographical references (leaves 151-159).
36

Tectono-stratigraphic and climatic record of the NE Arabian Sea

Calvès, Gérôme. January 2009 (has links)
Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on June 3, 2009). Includes bibliographical references.
37

Location of sub-fresnel scale mineral targets in the subsurface /

Moffat, Lucky, January 2004 (has links)
Thesis (M.Sc.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 101-102. Also available online.
38

Re-evaluation of reflection seismology for archaeological investigation

Cross, Guy Matthew 05 1900 (has links)
During the last decade, archaeologists have widely accepted the use of geophysical exploration techniques, including magnetic, resistivity and electromagnetic methods, for pre-excavation site assessment. Although researchers were quick to recognize the potential of seismic techniques to provide cross-sectional images of the subsurface, early feasibility studies concluded that seismic methods were inappropriate due to restricted resolving power and the relatively small-scale nature of archaeological features. Unfortunately, this self-fulfilling prophesy endures and has largely discouraged subsequent attempts to exploit seismic methods for archaeological reconnaissance. Meanwhile, however, seismic technology has been revolutionized in connection with engineering, groundwater and environmental applications. Attention to detail in developing both instrumentation and data acquisition techniques has yielded a many-fold improvement in seismic resolving power. In light of these advances, this dissertation re-examines the potential of reflection seismology for archaeological remote sensing. It is not the objective of this dissertation to deliver an unequivocal pronouncement on the ultimate utility of reflection seismology for the investigation of archaeological sites. Rather, the goal has been to establish a sound theoretical foundation for objective evaluation of the method's potential and future development. In particular, a thorough theoretical analysis of seismic detection and resolution yields practical performance and identifies frequency response characteristics associated with optimum resolution. Findings have guided subsequent adaptation, development and integration of seismic instrumentation, resulting in a prototype system for high-resolution seismic imaging of the shallow subsurface. Finally, to assess system performance and the suitability of optimum offset data acquisition techniques, a full-scale subsurface model has been constructed, allowing direct comparison between experimental soundings and known subsurface structure. Results demonstrate the potential of reflection seismology to resolve near-surface features on the scale of archaeological interest. Moreover, despite conventional wisdom that the groundpenetrating radar method possesses vastly superior resolving power, acquisition of coincident radar soundings demonstrates that the two techniques provide comparable resolution. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
39

Structure and regional tectonic setting across the Atlantic Coastal Plain of northeastern Virginia as interpreted from reflection seismic data

Pappano, Phillip A. 12 September 2009 (has links)
This study is a geophysical investigation that uses reflection seismic and potential field data to contribute to the development of a structural model of the North American Atlantic Passive Margin beneath the Atlantic Coastal Plain of northeastern Virginia. Specifically, this study focuses between 37.5° and 38.5° north latitude and 75.5° and 77.5° west longitude. The geophysical data include two seismic lines that were reprocessed at the Regional Geophysics Laboratory at Virginia Polytechnic Institute and State University. In addition, gravity modelling is performed in order to test the model developed from the seismic data. Several important results have been achieved from this study. Lower Cretaceous fluvial sediments are less reflective than the overlying marine sequence. This observation is most obvious toward the east, particularly on line CF-1. Reverse faulting, which might be related to movement within the basement, is observed in at least one location on line NAB-11A, near Loretto, VA. Curiously, the dip is in the opposite direction of other reverse faults observed within the coastal plain. The thickness of Triassic strata in the Taylorsville basin is constrained by seismic reflection data and gravity modelling. Results indicate that the basin is approximately 3 km deep. The strata within the basin appear to be poorly reflective except where they locally onlap the bottom of the basin, which is marked by a prominent reflector that is interpreted to be a diabase sill associated with Jurassic magmatism. In addition, the basin appears to be intruded by moderately dipping dikes that were fed by the sill. The occurrence of basaltic material within the basin is confirmed by well log data. Probably the most important result of this study is the tectonic implications of prominent, arcuate potential field anomalies and their relationships to changes in midcrustal reflectivity observed on the east side of line NAB-11A. Gravity modelling confirms the likelihood of a nearvertical, anomalous, mafic mass that extends to the Moho. This observation is supported by the loss of contiguous reflections in this area. A similar observation was made along the southern extension of the same anomaly by Coruh and others (1988) who proposed that this feature is a dike swarm associated with Mesozoic rifting. It is proposed here that this body also could be an ancient Mesozoic magma chamber that collapsed during cooling after the Atlantic margin passed into the drift sequence. / Master of Science
40

Analyzing deep-water near seafloor geology with chirp sonar sub-bottom profiles : Green Canyon, Gulf of Mexico

Hernandez, Jaime, 1968- 25 June 2015 (has links)
The study area is located on the continental slope in the Green Canyon deep-water area of the Gulf of Mexico. This area is being investigated by the Bureau of Economic Geology as part of several active gas hydrate studies across the area. The chirp sonar profiles used in my study were collected with an Autonomous Underwater Vehicle (AUV) utilizing a frequency-modulated seismic (sonar) source that emitted a 2 to 8 kHz sweep (chirp) frequency signal (wavelengths less than 2 meters). The recording time is limited to about 50 milliseconds, with time zero occurring at the altitude of the AUV about 50 meters above the seafloor. The signal images to about 40 meters below the seafloor, and profiles are as long as 5 km. An interpretation of deep-water, near sea-floor geology has been conducted using both chirp sonar profiles and multibeam bathymetry. Seismic reflections from within the shallow sediments are caused primarily by contrasts in density, rather than acoustic velocity. Reflections were successfully simulated using a model with a constant velocity of 1560 m/s and densities of 2.1 g/cc for sand, 1.4 g/cc for mud, and 1.7 g/cc for silty sand. The chirp sonar profiles imaged near-seafloor geology at nearly a meter scale and allowed for detailed interpretation. The interaction of soft sediment deformation, creep movement and neo-tectonic activity related to gas expulsion controlled the actual topography of the sea-floor. The geologic time represented in the 50 milliseconds of chirp data recorded with the AUV, which is about 40 meters of depth, is approximately 0.050 Ma. B.P., consistent with a depositional rate of 0.8 meters per 1000 years. Reflection patterns are interpreted to be related to fluctuations in sea level. High reflectivities (density contrasts) are interpreted to be deposited during the last sea level low stand, and low reflectivities are interpreted as sedimentation during the last high stand. Sediments deposited during the low stand are proximal while others are distal, deposited in deeper water environments. Shallow structures observed in the chirp sonar profiles are mainly related to gas mobilization mechanisms, which shaped the topography of the seafloor in conjunction with soft sediment deformation and creep movement. The geomorphic features are related in some cases to gas expulsion zones such as pockmarks and mud volcanoes. Other structures are related to soft sediment deformation and creep mobilization. Soft sediment deformation is confined to the deepest part of the minibasin, while the other features are not depth dependent. Highly deformed intervals at the bottom of the sequence seem to control subsequent sedimentation. / text

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