• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 645
  • 538
  • 261
  • 3
  • 3
  • 1
  • Tagged with
  • 3126
  • 749
  • 261
  • 247
  • 247
  • 235
  • 131
  • 129
  • 122
  • 115
  • 114
  • 113
  • 110
  • 109
  • 101
  • 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.

The Swansea Valley disturbance

Weaver, J. D. 1972 (has links)
No description available.

Novel applications of airborne LiDAR and multispectral data for high-resolution geological mapping of vegetated ophiolitic rocks and sedimentary cover, Troodos Range, Cyprus

Grebby, Stephen Robert 2011 (has links)
Practical and financial constraints associated with traditional field-based mapping are often responsible for the production of coarse-scale geological maps that lack detail and have inaccurately defined lithological contacts. Although remote sensing offers potential solutions to these constraints, conventional use of remotely sensed data is only effective when applied to barren terrain because just small amounts of vegetation cover can obscure or mask the underlying geological materials and structures. In this thesis, novel algorithms that utilise airborne Light Detection And Ranging (LiDAR) data and airborne multispectral imagery are applied to high-resolution geological mapping of vegetated ophiolitic rocks and sedimentary cover in the northern Troodos Range (Cyprus) with the aim of demonstrating their potential application to any geological setting. These novel algorithms involve quantification of geobotanical and topographical characteristics that are generally distinct for different lithological units, followed by automated image classification based upon these characteristics. Whilst the algorithms that individually exploit the geobotanical associations and the correlation between lithology and topography are capable of generating maps that are more detailed and have more accurately defined contacts than the existing geological maps of the study area, an integrated approach was found to significantly enhance the lithological mapping performance. Moreover, despite widespread vegetation cover, it is also shown that airborne LiDAR data and airborne multispectral imagery can be utilised to extract detailed and accurate structural information that is consistent with field-based data. Overall, the novel application of airborne spectral imagery and airborne LiDAR data has significant potential to aid accurate and high-resolution 1:5000-scale geological mapping over large areas of vegetated or non-vegetated terrain.

The northern boundary of the Ikertoq shear belt, west Greenland

Grocott, John 1977 (has links)
No description available.

Fracture mechanics of volcanic eruptions

Matthews, C. 2009 (has links)
Seismology is a key tool in the forecasting of volcanic eruptions. The onset of an eruption is often preceded and accompanied by an increase in local seismic activity, driven by fracturing within the edifice. For closed systems, with a repose interval of the order of a century or more, this fracturing must occur in order to create a pathway for the magma to reach the surface. Time-to-failure forecasting models have been shown to be consistent with seismic acceleration patterns prior to eruptions at volcanoes in subduction zone settings. The aim of this research is to investigate the patterns in seismic activity produced by a failure model based on fundamental fracture mechanics, applied to a volcanic setting. In addition to the time series of earthquake activity, statistical measures such as seismic b-value are also analysed and compared with corresponding data from the field and laboratory studies. A greater understanding of the physical factors controlling fracture development and volcano-tectonic activity is required to enhance our forecasting capability. The one dimensional, fracture mechanics grid model developed in this work is consistent with the theory of growth and coalescence of multi-scale fractures as a controlling factor on magma ascent. The multi-scale fracture model predicts an initial exponential increase in the rate of seismicity, progressing to a hyperbolic increase that leads to eruption. The proposed model is run with variations in material and load properties, and produces exponential accelerations in activity with further development to a hyperbolic increase in some instances. In particular, the model reproduces patterns of acceleration in seismicity observed prior to eruptions at Mt. Pinatubo (1991) and Soufriere Hills (1995). The emergence of hyperbolic activity is associated with a mechanism of crack growth dominated by interaction and coalescence of neighbouring cracks, again consistent with the multi-scale fracture model. The model can also produce increasing sequences of activity that do not culminate in an eruption; an occurrence often observed in the field. Scaling properties of propagating fractures are also considered. The seismic bvalue reaches a minimum at the time of failure, similar to observations from the field and measurements of acoustic emissions in the laboratory. Similarly, the fractal dimension describing the fracture magnitude distribution follows trends consistent with other observations for failing materials. The spatial distribution of activity in the model emerges as a fractal distribution, even with an initially random location of fractures along the grid. Significant shifts in the temporal or spatial scaling parameters have been proposed as an indication of change in controlling factors on a volcanic system, and therefore represent a relatively unexplored approach in the art of eruption forecasting.

Reconstructing Buried Alluvial Landscapes : The Application of Multiple Geophysical and Geoarchaeological Techniques

Mansfield, Carol 2007 (has links)
No description available.

Sedimentary studies in Lake Windermere

Holmes, P. W. 1964 (has links)
Late Quaternary sediments, soils,and parent rocks in and around the Windermere North Basin are studied by modern sedimentological techniques. Tho data obtained is examined statistically. Till points, scattered randomly on the Sand/silt/clay triangle, were redistributed into a "still later group", glaciolacustrine clays and main Windermere sediments; and a coarse fluvioglacial group which is better sorted and more rounded than the till. Fine sands, negatively skewed due to finer admixtures, typify certain lake environments. Beach deposits are better sorted and more rounded than the till from which they were partly derived; they are more rounded and coarser on the eastern exposed beaches than on sheltered ones; they are positively skewed due to inefficient fluviatile saltation. Three assumptions: a. Flocculation caused real mechanical bimodality of organic sediments. b. Spasmodic sedimentation was by underflowing "turbidity" currents during storms. c. Deposition occurred when settling (discrete or flocculated) overcame mechanical dispersal. Loss of river water impetus, and organic content and biological activity, controlled Poet Glacial sed1mentation. The relative importance of the two main rivers has alternated. Two basic mineralogical populations formed Late Quaternary material: a)Pink Late Glacial form, non hydrated. Post Glacial form, illite and aluminosilicates, hydrated and flocculated due to organic content and acidic environment (occurs up to 0.020 mm). b) Silt. Chloritic rock fragments (magnesium rich ripidolite, iron rich thuringite); calcite was removed from all but buried varves by Post Glacial acid corrosion. A marked change in lake sedimentation occurred with the spread of plant growth at the end of Late Glacial times 11,000 years ago. Controlled erosion, flocculation, and a high organic content characterised Post Glacial reddish gyttja sedimentation. Human settlement in the last 200 years caused further changes: accelerated erosion due to forest removal, reducing lakewater conditions due to sewage caused stronger flocculation in the blackish surface ooze.

The analysis of seismic attenuation spectra in rock mass characterisation : a case study at Acklington opencast coal site

Young, R. P. 1981 (has links)
No description available.

Seismic hazard assessment in Pakistan

Rehman, Khaista 2010 (has links)
No description available.

The geology of the region between the Alness River and the Dornoch Firth

Armstrong, Matthew 1964 (has links)
The stratigraphy, petrography and structure of the Old Red Sandstone between the Alness River and the Dornoch Firth have been examined in detail.

Towards using seismic anisotropy to interpret ductile deformation in mafic lower crust

Tatham, Daniel John 2008 (has links)
The lower crust forms an important geodynamic control in continental tectonics and the communication and coupling of kinematics between surface and deep-Earth processes. An understanding of the relationship between seismic properties, finite strain and fabric orientation thus provides a useful tool in the remote sensing and interpretation of deformation in the lower crust. This thesis outlines a work-flow model by which the seismic properties of a single and representative lower crustal lithology can be calculated and calibrated against finite strain from petrofabric development across a strain gradient. The work-flow model constitutes a multi-disciplinary approach, incorporating field mapping and sample collection, experimental petrofabric determination, and seismic modelling. A review of compositional estimates of the deep crust, including xenoliths, exposed sections and estimates from wide-angle seismic profiles, indicates the importance of mafic lithologies. The Laxfordian-age high-grade shear zone at Upper Badcall, NW Scotland, exhibits a strain gradient in a deformed doleritic Scourie dyke (Lewisian complex) that intersects the zone at a high angle. From an analysis of field data from detailed mapping, the shear zone is shown to be characterised by generally simple shear, but where the tectonic movement direction varies transversely across the shear zone. Calculation of the strain profile across the deformation zone gives shear strains, y up to 57, but with y < 15 being perhaps more realistic. Cumulative displacements total ~1000m left-laterally, and ~600m vertical displacement, north-side up. Nine samples were collected across the shear zone in the mafic dyke, representing a strain gradient from undeformed protolith to the highest recorded stains. The sample suite is characterised as a hornblende-plagioclase-quartz aggregate that develops macroscopic planar and linear fabrics with strain, from an essentially isotropic protolith. Quantification of the aggregate lattice preferred orientation (LPO) using electron backscatter diffraction (EBSD) showed the dominance of fabric development in the hornblende phase, with (100) poles clustering forming normal to the foliation plane and [001] axes parallel to the tectonic X direction. Plagioclase and quartz retained random fabrics from the wall-rock protolith with increasing finite strain. The hornblende LPO fabric, described by the texture index, J, shows a positive logarithmic relationship with strain, where LPO intensity saturated by y ~10. The strain-calibrated quantitative petrofabric description of each sample is used to calculate their aggregate elasticity tensors (Cij) via a Voigt-Reuss-Bill average, and from which seismic properties are derived using Christoffel's equation. Hence, a framework of petrofabric- and strain-calibrated seismic properties is described for a strain gradient in a representative high-grade mafic lithology. P-wave anisotropies up to ~10% are-recorded in the most deformed samples with Vsmax typically between 6.42-6.63kms/-1. S-wave anisotropies record up to 7.23% AV, in the most deformed samples, with Vpmax ranging between 3.62-3.75kms-1 for all samples. The relationship between petrofabric-derived seismic anisotropy and finite strain across the sample suite show a positive relationship, approximated by a logarithmic function, whereby P- and S-wave anisotropy exhibit a steep positive gradient with strain up to y~10. The sample-wise framework of petrofabric- and strain-calibrated seismic properties is interpolated to estimate the continuum relationship between seismic properties, finite strain and petrofabric orientation. In a move to illustrate the application of results in seismic and structural modelling, case study models of crustal deformation are presented for the eastern Basin and Range province, the North Sea rift, and Tibet. Models are promising in their ability to differentiate between regions of lower crust characterised by a uniform mafic composition but different finite strain state and/or petrofabric geometry, although multiple seismic survey methods may be needed to fully interpret results in terms of strain and fabric orientation. In summary, a multidisciplinary approach combining field mapping and sampling, petrofabric characterisation with EBSD, and seismic modelling provides an efficient and reproducible work-flow for the determination of petrofabric-derived strain-calibrated seismic properties of lower crustal materials.

Page generated in 0.0273 seconds