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

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

This study describes the tectono-stratigraphic and climatic record of the NE Arabian Sea during the Cenozoic.  Compilation of regional knowledge and subsurface observations has in this thesis provided new interpretations and insights into the records present along this passive margin.  The first is the rifting period (80-65 Ma) and the identification of a syn-rift volcanic sequence, comparable to other volcanic rifted margins.  This is followed by the record of a drift sequence (~65 Ma to present day), composed of extensive carbonate platforms and an infill sequence of siliciclastic deposits.  The analysed drift sequence (sink) is partly the result of the erosion of the hinterland (source) characterised by the India-Eurasia continent-continent collision.  Influence of regional climate and/or tectonic forces on the accumulation rate in the sink was tested, but not conclusive as the study area (Upper Indus Fan) covers only a limited part of the sedimentary record of the Indus Fan.  The thermal regime of the western margin of India is sparsely sampled, but once analysed, allows the definition of first order constraints on multiple rifting events.  The post-rift subsidence of the margin is slow and anomalous for >28 m.y. after break-up, potentially in relation with vigorous asthenospheric convection and a sharp ocean-continent boundary.  Past and present fluid flow is recorded in the sedimentary sequence of the Upper Indus Fan.  The first is related to gas hydrate occurrence and is the result of the migration of fluids by a plumbing system to the shallow subsurface, expressed by bottom-simulating reflections crosscutting stratal reflections.  A longer term fluid migration is recorded in this basin by the longest lived (~22 m.y.) mud volcano field recorded to date.

Several seismic reflection surveys were conducted in the late 1980s and early 1990s under the auspices of the SA National Geophysics Programme. These surveys targeted the Bushveld Complex, Limpopo Mobile Belt (Limpopo Province), Witwatersrand Basin, Vredefort Dome and the Beattie magnetic anomaly (BMA) in the Southern Karoo. The ~100 km seismic reflection profile described in this study (SAGS-03-92) covers the BMA, the Southern Cape Conductive Belt (SCCB) and the Karoo/Cape Fold Belt boundary. The profile runs from approximately Droëkloof in the south to Beaufort West in the north along the N12 national road. The profile was acquired in 1992, but the complete profile was not interpreted or published prior to this study. The purpose of this study is to successfully reprocess the data and to do a structural and stratigraphic interpretation in order to try and understand the geological history and processes that led up to the formation of the rocks in that area. SAGS-03-92 reveals a clear image of the crust in the southern Karoo. The crust is interpreted to be around 37 km thick in the area of investigation and can be classed into three parts: upper crust, middle crust and lower crust. The upper crust consists of the Karoo and Cape Supergroup rocks that dip slightly to the south. This interpretation has been confirmed by two deep boreholes (BH No. 3 and KW 1/67). The seismic fabric shows quite a strong character in the upper crust and the interpreted boundaries between the different lithologies (The Table Mountain, Bokkeveld and Witteberg Groups of the Cape Supergroup and the Dwyka, Ecca and Beaufort Groups of the Karoo Supergroup) are for the most part quite easy to identify. Within the Cape Fold Belt (CFB), however, the seismic character becomes distorted in such a way that it is very difficult to make out any features. This is possibly due to the severe faulting and folding that occurred when the CFB formed. An unconformity that can continually be followed throughout the profile (although it disappears in the south of the profile possibly due to deformation when the CFB formed) separates the upper crust from the middle crust and the unconformity is clearly indicated by a strong series of reflectors on the seismic profile. The middle crust is interpreted to consist of granitic-gneisses belonging to the Bushmanland Terrane (part of the Namaqua-Natal Belt (NNB)). The seismic profile suggests that the NNB gneisses continue beneath the Cape Fold Belt. The seismic fabric dips steeply to the north. The middle crust also hosts the source of the Beattie Magnetic Anomaly (BMA). There is an area of high reflectivity under the BMA on the seismic profile that differs significantly from the surrounding seismic character. This area is characterised by a beanshaped cluster of strong reflections dipping north and south. It is ~10 km wide, with a thickness of ~8 km and occurs at a depth of ~6 km to ~10 km. The lower crust is interpreted to consist of either granites belonging to the Areachap Terrane, Richtersveld or Kheis Province (NNB) or rocks belonging to the Kheis Province. The seismic fabric of the lower crust dips moderately to the south. The Moho is recognised at ~37 km depth at ~68 km from the south of the profile, but for the rest of the profile, it is unclear where the Moho is encountered. The research done for this study correlates well with work done under the auspices of Inkaba yeAfrica, especially the work done by Ansa Lindeque

Three dimensional (3-D) seismic reflection surveying is accepted as the preferred method for imaging complex geology for proving and developing commercial oil and gas fields. However, the cost of 3-D seismic recording and processing is substantial and often can be as expensive as the cost of production drilling. This is particularly the case for land oil field development, where the cost of 3-D surveying is often unacceptably high. Such high costs also restrict its application in coal exploration, where 2-D seismic methods have long been accepted.During the early 1980's, a low fold technique for recording land 3-D data was devised which offered significant cost savings. The technique was adapted by the author for land 3-D surveying over coal fields. Inherent in the technique was a requirement that the data must have a high signal-to-noise ratio, which is not generally the case in land surveying due to the presence of strong source generated surface wave noise. A further major impediment to the technique was its inability to perform an acceptable stacking velocity analysis because of the low number of seismic traces generated. This thesis defines three data collection and processing advancements in low fold 3-D technology which go some way towards resolving these impediments.The first advancement is a method to enhance the signal-to-noise ratio of the stacked seismic data, and consists of a Radon-based transform which stacks shot domain data along a curved trajectory, thereby attenuating surface waves on swath recorded data. This transform is termed the 'Radial Transform' of 3-D data.The second advancement is a statics method to improve the stacked image from a low number of input traces. The method uses the concept that if both the reflected and refracted waves pass through a weathering layer with very similar travel paths, then static corrections to remove the ++ / effects of weathering variations on the refraction travel times would be very similar to those required for the reflections. This method, which was patented, is used equally for both 2-D and 3-D field data, and is regularly used in high resolution seismic processing for coal at Curtin University.The third advancement resolves the problem of azimuthal variation of stacking velocities. By predicting the true reflector dip and its azimuth, apparent dip can be included in the normal moveout equation, which is named the Generalized Moveout equation. The requirement for an azimuthally dependent stacking velocity is then no longer an impediment in low fold 3-D processing of coal data.After developing these transforms and applying them to synthetic data, they were tested with success on modelled field data. All field data used within this thesis were either recorded in the field by the author, or were produced with a physical modelling system, which was built by the author at the University of Houston and later at Curtin University.Results indicate that the procedures described in this thesis enable the low fold 3-D technique to be used as a viable method for recording seismic data when survey economics are a major issue. Furthermore, all three advancements are suitable for application in conventional two dimensional (2-D) and swath seismic surveying.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2000. / Bibliography: leaves 114-119.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xi, 149 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 118-124).

The seismic reflection method has been used extensively in mineral exploration and for imaging crustal structures within hardrock environments. In this research the seismic reflection method has been used and studied to address problems associated with hardrock settings. Papers I and II, address delineating and imaging a sulfide ore body and its surrounding rocks and structures in Garpenberg, central Sweden, at an active mine. 3D ray-tracing and finite-difference modeling were performed and the results suggest that although the detection of the ore body by the seismic reflection method is possible in the area, the presence of backfilled stopes in the mine makes seismic imaging of it difficult. In paper III the deeper structures of the Pärvie fault system in northern Sweden were revealed down to about 8 km through 2D seismic reflection profiling. The resulting images were interpreted using microearthquake data as a constraint. Based on the interpretation, some locations were suggested for future scientific deep drilling into the fault system. In paper IV, the seismic signature of complex geological structures of the Cue-Weld Range area in Western Australia was studied using a portion of a deep 2D seismic reflection profile. The pronounced reflections on the seismic images were correlated to their corresponding rock units on an available surface geological map of the study area. 3D constant velocity ray-tracing was performed to constrain the interpretation. Furthermore, the proposed structural model was tested using a 2D acoustic finite-difference seismic modeling method. Based on this study, a new 3D structural model was proposed for the subsurface of the area. These studies have investigated the capability of the seismic reflection method for imaging crustal structures within challenging hardrock and complex geological settings and show some its potential, but also its limitations.

One of the important goals in petroleum exploration and production is to make quantitative estimates of a reservoir’s properties from all available but indirectly related surface data, which constitutes an inverse problem. Due to the inherent non-uniqueness of most inverse procedures, a deterministic solution may be impossible, and it makes more sense to formulate the inverse problem in a statistical Bayesian framework and to fully solve it by constructing the Posterior Probability Density (PPD) function using Markov Chain Monte Carlo (MCMC) algorithms. The derived PPD is the complete solution of an inverse problem and describes all the consistent models for the given data. Therefore, the estimated PPD not only leads to the most likely model or solution but also provides a theoretically correct way to quantify corresponding uncertainty. However, for many realistic applications, MCMC can be computationally expensive due to the strong nonlinearity and high dimensionality of the problem. In this research, to address the fundamental issues of efficiency and accuracy in parameter estimation and uncertainty quantification, I have incorporated some new developments and designed a new multiscale MCMC algorithm. The new algorithm is justified using an analytical example, and its performance is evaluated using a nonlinear pre-stack seismic waveform inversion application. I also find that the new technique of multi-scaling is particularly attractive in addressing model parameterization issues especially for the seismic waveform inversion. To derive an accurate reservoir model and therefore to obtain a reliable reservoir performance prediction with as little uncertainty as possible, I propose a workflow to integrate 4D seismic and well production data in a Bayesian framework. This challenging 4D seismic history matching problem is solved using the new multi-scale MCMC algorithm for reasonably accurate reservoir characterization and uncertainty analysis within an acceptable time period. To take advantage of the benefits from both the fine scale and the coarse scale, a 3D reservoir model is parameterized into two different scales. It is demonstrated that the coarse-scale model works like a regularization operator to make the derived fine-scale reservoir model smooth and more realistic. The derived best-fitting static petrophysical model is further used to image the evolution of a reservoir’s dynamic features such as pore pressure and fluid saturation, which provide a direct indication of the internal dynamic fluid flow. / text

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