Settling basins can be shortened by using a stack of horizontal parallel plates which develop boundary layers in which sedimentation can occur. The purpose of this study is to examine the design parameters for such a system and to apply this approach to a fish rearing channel in which settling length is strictly limited. Flow between parallel rough and smooth plates has been modelled together with sediment concentration profile. Accurate description of boundary layer flow requires the solution of Navier-Stokes equations, and due to the complexity of the equations to be solved for turbulent flow some assumptions are made to relate the Reynolds stresses to turbulent kinetic energy and turbulent energy dissipation rate. The simplified equations are solved using a numerical method which uses the approach given by the TEACH code. The flow parameters obtained from the turbulent flow model are used to obtain the sediment concentration profile within the settling plates. Numerical solution of the sedimentation process is obtained by adopting the general transport equation. The lower plate is assumed to retain sediments reaching the bottom. The design of a sedimentation tank for a fish rearing unit with high velocity of flow has been investigated. The effectiveness of the sedimentation tank depends on the uniformity of flow attained at the inlet, and experiments were conducted to obtain the most suitable geometric system to achieve uniform flow distribution without affecting other performances of the fish rearing unit. The main difficulties to overcome were the heavy circulation present in the sedimentation tank and the clogging of the distributing system by suspended particles. Several distributing systems were investigated, the best is discussed in detail. It was concluded that a stack of horizontal parallel plates can be used in fish rearing systems where space is limited for settling sediments. Flow distribution along the vertical at the entrance to the plates determines the efficiency of the sediment settling process and a suitable geometrical configuration can be constructed to distribute the high velocity flow uniformly across the vertical. Numerical modelling of sediment removal ratio for flow between smooth and rough parallel plates has been calculated. The results show that almost the same pattern of sediment deposition occurs for both the smooth-smooth and rough-smooth plate arrangements. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The Queen Charlotte transform fault zone, which lies immediately east of the Queen Charlotte Islands, marks the boundary between the oceanic Pacific and the continental North American plates. Relative plate motions suggest that oblique underthrusting of the Pacific plate beneath North America may be presently occurring along this transform fault. To investigate this plate boundary and the implications of oblique subduction on crustal structure beneath the region, an onshore-offshore seismic refraction survey was conducted in 1983. The survey was designed to sample the crust beneath the Queen Charlotte Islands and across Hecate Strait to the mainland of British Columbia. Six ocean bottom seismographs and 11 land based stations were deployed along a 200 km line extending from 20 km west of the Queen Charlotte Islands to the mainland. Thirteen 540 kg and twenty 60 kg explosive charges were detonated along a 110 km long east-west line in the ocean to the west of the receivers. The multiple shots recorded on multiple receivers, all along the same line, effectively reverses the profile over some of its length. The objective of this study is to provide a model of the deep crustal structure beneath the fault zone, the Queen Charlotte Islands, and Hecate Strait. An exemplary subset of the extensive data set was selected to meet this objective. Beneath the deep ocean the Moho dips at about 2° to the east. At the Queen Charlotte terrace, a 25 km wide zone immediately west of the active Queen Charlotte fault, the dip of the Moho increases to about 5°. The crust is about 12 km thick at the terrace and 18 km thick at the eastern edge of the Queen Charlotte Islands, and in excess of 30 km thick at the mainland. The terrace unit itself is divided into two units - an upper unit with low velocity (4.1 km/s) and high gradient (0.3 km/s/km) and a lower unit with a high velocity (6.5 km/s) and a low gradient (0.05 km/s/km). This model, while not definitive, supports the interpretation of oblique shallow underthrusting of the Pacific plate beneath the Queen Charlotte Islands. The upper terrace unit could represent a sedimentary accretionary wedge and the lower terrace unit - the subducting slab. A model in which compression across the Queen Charlotte transform fault zone is taken up by deformation of the Queen Charlotte Islands in the form of crustal shortening and thickening is not compatible with the thin crust beneath the islands and Hecate Strait. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Io, the most volcanically active body in the solar system, also has some of the tallest and steepest mountains. The mountains seem to be tectonic in origin, yet the methods of their formation have not been decisively constrained and their associations with volcanic paterae are yet unclear. We have compiled global spatial statistics on mountain dimensions and orientations, lineations attributed to structures, straight patera margins, and patera dimensions in order to better define their genetic relationships and the mechanisms forming each type of feature. Additionally, we have produced 4 regional structural maps of mountain complexes and have proposed tectonic histories. Global statistics show that paterae and mountains and their associated lineations are more common at low latitudes and that lineations attributed to tectonics have preferred azimuths of 45° and 135°, whereas straight patera margins and azimuths appear more random. Additionally, tectonic lineations tend to cluster to those of similar types and are smaller when closer together. Mountains in general on Io are isolated, varied in size and shape, and have no significant geographic patterns in those variations. These results may indicate that global-scale processes are involved in forming Io's tectonic structures, but that the diversity of mountain characteristics and the collapse of paterae adjacent to mountain complexes may be more regionally controlled. Mapping of the Hi'iaka, Shamshu, Tohil, and Zal regions has shown that Io's mountains reside in large, faulted-bounded crustal blocks, which have undergone modification through local responses of subsurface structures. Strike-slip motion along reactivated faults has led to the formation of both transpressional and transtensional features, creating tall peaks and low basins, some of which are now occupied by paterae. Subsurface structures play a large role in Io's mountain diversity. Based on interpretation of statistical results and on our localized mapping, we propose that Io's mountains result from a combination of crustal stresses involving both global and local-scale processes. Multiple faults and fractures in a variety of orientations formed in Io's lithosphere, created over billions of years by stresses imposed by volcanic loading and tidal flexing. These faults have been progressively buried over time under multiple layers of volcanic material. Stresses continuing from loading and tidal massaging sometimes occur at oblique angles to pre-existing faults, reactivating them as reverse, normal, or strike-slip faults. Because of this, large, cohesive fault-bounded blocks have undergone both transpressional and transtensional modification. Further degradation of mountains has also occurred from extensive mass wasting, gravitational collapse, and erosion by sublimation and sapping of sulfur-rich layers within the crust. This model of fault-bounded blocks being modified by continual stresses and local structural response accounts for the variation and patterns of mountain sizes, shapes, and orientations, along with their isolation and interactions with other features. It presents an explanation for the influence of global and regional tectonics and a more detailed account of the formation of some of Io's remarkable mountains.

The Qadimah Fault has been mapped as a normal fault running through the middle of a planned $$$50 billion city. For this reason, there is an urgent need to evaluate the seismic hazard that the fault poses to the new development. Although several geophysical studies have supported the existence of a fault, the driving mechanism remains unclear. While a fault controlled by gravity gliding of the overburden on a mobile salt layer is unlikely to be of concern to the city, one caused by the continued extension of a normal rotational fault due to Red Sea rifting could result in a major earthquake. A number of geomorphology and geodetic techniques were used to better understand the fault. An analysis of topographic data revealed a sharp discontinuity in slope aspect and hanging wall tilting which strongly supports the existence of a normal fault. A GPS survey of an emergent reef platform which revealed a tilted coral surface also indicates that deformation has occurred in the region. An interferometric synthetic aperture radar investigation has also been performed to establish whether active deformation is occurring on the fault. Ground movements that could be consistent with inter-seismic strain accumulation have been observed, although the analysis is restricted by the limited data available. However, a simple fault model suggests that the deformation is unlikely due to continued crustal stretching. This, in addition to the lack of footwall uplift in the topography data, suggests that the fault is more likely controlled by a shallow salt layer. However, more work will need to be done in the future to confirm these findings.

Our knowledge of Earth's structure and dynamics is owed, in large part, to techniques that allow us to infer the physical properties of rocks based on observations made near the surface. In particular, passive seismic imaging relies on natural sources of elastic wave energy (typically earthquakes) to illuminate Earth's interior. The frequency-dependent dispersive characteristics of surface waves from earthquakes provides a valuable constraint on the depth heterogeneity beneath the surface, which can be used to infer structure of the lithosphere (i.e., tectonics). The first part of this thesis develops novel tools for passive seismic imaging considering surface-wave dispersion. Specifically, Bayesian (probabilistic) methods are developed that provide rigorous uncertainty quantification. The ability to estimate the directional dependence of surface-wave speeds (i.e., seismic anisotropy) is demonstrated. Furthermore, a general approach for considering circular (wrapped) data, such as surface-wave phase measurements, is developed and applied to estimate the average dispersion between pairs of seismic stations. These ideas are applied to data recorded at seismic stations over British Columbia, Canada, to produce a large volume of data products that will help improve our understanding of the tectonics throughout the region. The second part of this thesis investigates the structural and mechanical conditions in subduction zones, where tectonic plates collide and one plate is thrust beneath the other. Specifically, a type of passive seismic imaging based on recordings of body waves from distant earthquakes (known as receiver functions) is used to infer subduction zone structure in relation to the coupling between tectonic plates. Receiver function data calculated for stations over the Cascadia subduction zone (southwestern Canada) suggest that episodes of slow slip on the plate interface occur in tandem with changes in mechanical conditions. Receiver function data calculated for stations over the Hikurangi subduction zone (New Zealand) suggest that stress and deformation along the margin are spatially linked to plate coupling. These results improve our understanding of the dynamics of these tectonic systems, including the seismic hazards that they pose.

I present new models of the elastic structure of the Pacific upper mantle that address the formation and evolution of oceanic plates. Using a surface-wave dispersion dataset, I perform anisotropic tomography to construct two-dimensional phase-velocity maps and three-dimensional velocity models of the Pacific basin. My three-dimensional elastic models describe both the radial and azimuthal anisotropy of seismic waves. In order to constrain these models, I develop regularization techniques that incorporate a priori information about the nature of the oceanic upper mantle, including both the age dependence of seismic velocities and the expected scaling relationships between azimuthal anisotropy parameters derived from realistic peridotite elastic tensors. I observe a strong cooling signal in the upper-mantle seismic velocities that is consistent with halfspace cooling of the lithospheric plate; deviations from this simple cooling signature are related to the influence of mantle plumes or other thermal alteration of the lithosphere. As plate age increases, the depth to the thermally controlled lithosphere-asthenosphere boundary increases as well. This thermal boundary, as seen in the negative gradient in seismic velocities, is consistent with the depth at which there is a transition in anisotropy fast-axis orientation. This change in anisotropy orientation is due to the transition from frozen-in lithospheric anisotropy to asthenospheric anisotropy that is related to geologically recent shear beneath the base of the plate. The anisotropy orientations and strength that we observe throughout the plate are only consistent with A-type olivine fabric. There are regions where anisotropy orientations do not align with paleospreading directions in the lithosphere or absolute-plate-motion in the asthenosphere, suggesting that small-scale convection, mantle flow, and plumes could all lead to changes in the orientation of seismic anisotropy. There is a dependence on the strength of anisotropy on spreading rate at shallow depths; this implies that corner flow at faster-spreading ridges is more effective at aligning olivine crystals in the direction of shear. I also present a new set of local surface-wave amplification maps spanning the contiguous United States. I perform a synthetic-tomography experiment in order to assess our ability to resolve variations in surface-wave amplification due to variations in local elastic structure. Local amplification derived from synthetic seismograms is very highly correlated with direct predictions of amplification, suggesting that we are able to resolve this signal well and that local amplification observations reflect elastic structure local to the station on which they are measured. Local amplification can be used as a complementary constraint to phase velocity in order to map upper-mantle elastic structure.

The deformation mechanisms responsible for the extension and rifting in Basin and Range extension over the past ~36 Ma, and their relative importance remain debated. Slab rollback, lithospheric body forces, and relative plate motions have all been shown to contribute, but the relative importance of each mechanism is not fully understood. Here, we build three-dimensional (3D) steady state geodynamic models to simulate the full tectonic reconstruction of Basin and Range extension and compare these results with known geologic field observations and other detailed reconstructions of surface deformation. Our modeling approximates lithospheric deformation through Stokes flow in a spherical cap of variable viscosities. By applying reconstructed boundary conditions, crustal thickness, and surface elevation at 17 Ma, and varying lithospheric viscosity we map out the predicted response of the surface motions and lower crustal flow for different assumed lithospheric viscosity contrasts and investigate the origin of core complex formation. Comparisons between predicted model deformation and geologic field observations from metamorphic core complexes and exposed fluorite deposits indicate: (1) The primary driving force of the formation of geologic features in the western US is regional gravitational collapse focused in the lower crust. Plate motions are second order by comparison at this time period and act to rotate velocities near the plate boundary. (2) A weak lower crust facilitates metamorphic core complex formation and extension in the Nevadaplano. Lateral extrusion of the lower crust serves as a mechanism for both core complex formation and the flattening of the Moho that is observed at present day. (3) Lower crustal flow is a contributes to the rotation and tilt of the Colorado Plateau and formation of the Rio Grande Rift.

No description available.

The Grenville Province represents a complex, highly metamorphosed orogenic belt at the southeastern margin of the Canadian Shield that is composed of different lithotectonic domains of various ages that have all been affected by the 1.0 Ga Grenville Orogeny. The present study focuses on one of the youngest regions, the Quebecia terrane, and through reconnaissance neodymium isotope mapping, investigates the extent of an old crustal block that predates the Grenville Orogeny. The Quebecia Terrane is found within Central Quebec and is a Mesoproterozoic arc terrane that was constructed around 1.5 Ga. Utilizing the Samarium-Neodymium dating method, previous research had identified a few isolated neodymium signatures of older crustal ages, and through reconnaissance mapping, several of these Paleoproterozoic crustal blocks are suggested to represent a single fragmented crustal panel. The study focused on more detailed mapping of these blocks in the areas of Baie Comeau, Forestville, Labrieville and Pipmuacan in Central Quebec. The full extent and connection between the fragments has been mapped as a series of Paleoproterozoic crustal blocks extending longitudinally through the Quebecia terrane. These blocks are embedded within the younger terrane, suggesting that the old panel was incorporated sometime during the accretion of Quebecia to Laurentia. It is possible that the old panel broke off from older Laurentian crust and reattached during the accretion of the Quebecia terrane via strike slip tectonics, implying that the Quebecia terrane itself consists of more than one accreted unit. The present study found that the older neodymium isotope signatures were consistent with the Berthe Terrane in the Manicouagan region to the north, providing evidence for the origin of the older panel within Quebecia. However, by invoking a division of Quebecia into a north and south segment, this implies a Composite Arc Belt model for the Central Grenville Province. / Thesis / Master of Science (MSc)

No description available.