Browsing by Author "Kocel, Eray"
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Item 3D Seismic Survey Design: Coil Shooting, Multi-Component (3C) Receivers with Gulf of Mexico and Caribbean Case Histories(2015-05) Kocel, Eray; Stewart, Robert R.; Mann, Paul; Sager, William W.; Baysal, EdipThe effectiveness of seismic imaging depends on numerous factors, beginning with how the data are acquired. The analyses presented in this theses show the importance of survey design, as individual parameters exert a strong influence over the resulting subsurface illumination. Survey design studies discussed here with different geological settings and geographical locations include: 1) Marine surveys with circular shooting for a subsalt target in the Gulf of Mexico, 2) Multicomponent land seismic survey designs for an unconventional resource, and 3) Integrated geophysical data analyses and survey design for a blind fault imaging at the 2010 Haiti earthquake epicentral area. In the case of marine surveys, the dual-coil design provides full-azimuthal coverage, whereas the Wide-azimuth surveys (WAZ) contain some acquisition footprints due to their straight-line geometry with limited-azimuthal coverage. Survey design optimization quantified the WAZ survey as having 20 % less illumination intensity than the dual-coil survey. For the multicomponent survey design, we analyzed the effects of VP/VS values (2, 4, and 6), target depth (800, 1,600, and 3,200 m) and orthogonal or slanted shot geometries. The updip shifting of the illumination area due to target layer inclination (5˚, 15˚, and 30˚) required longer offsets to fully capture the seismic data. Staggered (periodically shifted) receiver lines achieved smaller bin sizes (6.25 m vs 25 m) with a very little additional acquisition effort. We also consider a case history from Léogâne fan-delta in Haiti, where some of the worst shaking was located by the 2010 Haiti earthquake. This intense shaking of the fan-delta area was attributed to either activation of a blind thrust fault, ~4 km beneath the surface, or to a strike-slip motion along a shallow, ground-breaking fault. We acquired seismic, gravity, and GPS data which were integrated with remote sensing studies. Our integrated results indicated disruptions of the near-surface material in the Léogâne region. Survey design studies suggested that multiple 2D seismic lines with 6 km offsets and optional marine surveys may be required to image the proposed blind fault. This thesis suggests novel seismic survey designs for a variety of subsurface geologies.Item An Integrated Geophysical Study of the Northern Gulf of Mexico(2012-05) Kocel, Eray; Hall, Stuart A.; Casey, John F.; Bird, DaleThe end members of passive continental margins are characterized as non-volcanic or volcanic depending on the nature of the transition zone. Differences between these two types are usually reflected by the differences of the physical properties of the Ocean-Continent Transition (OCT). Gravity, magnetic, and seismic data used to investigate the crustal structure of a portion of the northern Gulf of Mexico. Six 800-km long, crustal cross sections have been constructed across the study area with 70 km spacing. Two-dimensional crustal models, comprising 7 layers have been developed to simulate the observed Free-air gravity anomalies. The density of each layer has been kept constant and the geometry of the individual layers modified to obtain a good match to the gravity data. Where possible the gravity models have been constrained by available seismic and magnetic data. Interpretations for the boundaries between different crustal types are delineated by modeling. The magnetic anomalies were used to define the extent of the transitional crust and interpreted as the effects of subaerial flood basalts. For this study OCT was defined as the region where the crustal thickness is greater than 9 km and less than 25 km. The average width of the OCT in the models is 250 km which is greater than that found in previous studies at other volcanic margins. To satisfy concerns that some magnetic anomalies may be due to sea-floor spreading, an alternative model with a narrower transition was constructed which matched the data equally well. In order to reconstruct the pre-extension position of Yucatan the stretched continental crust and transitional zone (restored back to 32 km thickness) across the northern margin, 15° of rotation about a pole south of Florida and 9° further rotation for southern Gulf of Mexico is required. Results from previous studies suggest that the Yucatan Block underwent an additional 20° of rotation due to sea-floor spreading along the restoration arc (total amount of 44° counterclockwise rotation). The results of this thesis supports some previous studies that concluded: (1) the nature of the margin can be classified as being volcanic passive margin and (2) plate reconstructions require counterclockwise rotation for the opening of Gulf of Mexico.