Conventional migration methods, including reverse-time migration (RTM) have two weaknesses: first, they use the adjoint of forward-modelling operators, and second, they usually apply a crosscorrelation imaging condition to extract images from reconstructed wavefields. Adjoint operators, which are an approximation to inverse operators, can only correctly calculate traveltimes (phase), but not amplitudes. To preserve the true amplitudes of migration images, it is necessary to apply the inverse of the forward-modelling operator. Similarly, crosscorrelation imaging conditions also only correct traveltimes (phase) but do not preserve amplitudes. Besides, the examples show crosscorrelation imaging conditions produce strong sidelobes. Least-squares migration (LSM) uses both inverse operators and deconvolution imaging conditions. As a result, LSM resolves both problems in conventional migration methods and produces images with fewer artefacts, higher resolution and more accurate amplitudes. At the same time, RTM can accurately handle all dips, frequencies and any type of velocity variation. Combining RTM and LSM produces least-squares reverse-time migration (LSRTM), which in turn has all the advantages of RTM and LSM. In this thesis, we implement two types of LSRTM: matrix-based LSRTM (MLSRTM) and non-linear LSRTM (NLLSRTM). MLSRTM is a matrix formulation of LSRTM and is more stable than conventional LSRTM; it can be implemented with linear inversion algorithms but needs a large amount of computer memory. NLLSRTM, by contrast, directly expresses migration as an optimisation which minimises the 2 norm of the residual between the predicted and observed data. NLLSRTM can be implemented using non-linear gradient inversion algorithms, such as non-linear steepest descent and non-linear conjugated-gradient solvers. We demonstrate that both MLSRTM and NLLSRTM can achieve better images with fewer artefacts, higher resolution and more accurate amplitudes than RTM using three synthetic examples. The power of LSRTM is also further illustrated using a field dataset. Finally, a simple synthetic test demonstrates that the objective function used in LSRTM is sensitive to errors in the migration velocity. As a result, it may be possible to use NLLSRTM to both refine the migrated image and estimate the migration velocity.

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The Norwegian rifted continental margin was formed by the breakup at 55Ma and earlier Mesozoic rifting of the North Atlantic. The continental margin reveals pre-breakup lithosphere deformation during the Triassic, Jurassic and Cretaceous Periods. This study examines the Lofoten, Vering and Mere margin segments in order to better understand the evolution of the Norwegian margin. Interpreted seismic crustal profiles have been analyzed to determine continental lithosphere thinning and upper crustal extension from the Triassic Period to present day. Continental crustal structure and thinning coupled with the location of both the ocean continent transition (OCT) and the continent ocean boundary (COB) have also been addressed. This study shows that the Norwegian rifted margin experienced breakup depth-dependent lithosphere stretching and thinning where whole lithosphere stretching and thinning exceeds that of the upper crust. Earlier pre- breakup lithosphere deformation during the Triassic, Jurassic and Early Cretaceous rifting is shown to be depth-uniform leading to intra-continental rift basin formation. The non-coaxial superposition of lithosphere thinning from the earlier intra-continental rift events with Early Tertiary breakup thinning has led to a complex and laterally varying distribution of thinned continental lithosphere. It is important to understand the structure and rifting history in order to partition the stretching and thinning of the Norwegian continental margin lithosphere. By these methods better predictions of the subsidence and heat flow histories of the Norwegian margin can be deduced.

Hyperalkaline (pH >11) spring waters across the Oman-UAE ophiolite have precipitated large-scale surface and subsurface freshwater carbonate deposits within and on mantle-sequence peridotites. Ten carbonate lithofacies have been identified that display a common stratigraphy across the region, with some on-going deposition. Alternating wet and arid climate periods, consistent with previous Quaternary climate data for Oman and the UAE, can be inferred from the morphologies and stratigraphy of carbonate lithofacies. Carbon and oxygen stable isotope ratios for individual lithofacies are consistent across the ophiolite, indicating uniform formation processes throughout the region. Modern carbonates actively precipitate via the drawdown of atmospheric CO2 into hyperalkaline groundwaters, indicated by very negative δ13C values (≈ –25‰) and δ18O (≈ –18‰) caused by kinetic fractionation. In contrast, ancient travertines display a much wider range in δ13C and δ18O, reflecting mixing of several C and O sources including atmospheric CO2, dissolved limestone CO32– and soil DIC. Radiocarbon data for ancient travertines show a series of stratigraphically impossible 14C “ages” which are interpreted to be due to the incorporation of a proportion of 14C-dead carbon. The sources of 14C-dead carbon are a mixture of dissolved limestone CO32–, soil DIC and the re-working of older carbonate deposits. The proportion of carbon from different sources must be taken into account when calculating sequestration rates of atmospheric CO2 into carbonates. The incorporation of 14C-dead carbon into carbonate lithofacies leads to a systematic offset in conventional radiocarbon ages towards older ages. Use of offset, older ages will cause underestimation of the rate of carbon sequestration, whilst the presence of 14C-dead carbon will cause overestimation of the volume of atmospheric carbon being stored. Age offsets in carbonates mean that sequestration rates taking into account all carbon in the system, e.g. from atmospheric or limestone CO32–, will be higher than previously thought.

Multiple prediction through inversion (MPI) is an effective method for seismic multiple attenuation. The research in this thesis aims to make the MPI method more practical for both free-surface and internal multiple attenuation. For free-surface multiple attenuation, the MPI scheme requires the input data to be dense and regularly sampled, and with one shot at each receiver position. In order to meet these requirements, I use a multilevel B-spline method for seismic data reconstruction. This method can perform regularisation and interpolation on seismic data without any prior-knowledge of models. For free-surface multiple attenuation on marine data, MPI can generate superior results compared to SRME (surface-related multiple attenuation). However, MPI is more computationally expensive due to the large amount of matrix operations involved. The conventional implementation addresses this by approximating the multiple model prediction operator as a pentadiagonal or a tridiagonal matrix. Tackle this problem by solving the full prediction operator using a Graphic Processing Unit (GPU), this accelerates the processing and improve the multiple attenuation results, especially for far-offset traces. As extensions of SRME for internal multiple attenuation, both the CFP (common-focus-point) technique and correlation method have problems. The results can be improved using the MPI method with GPU acceleration. The correlation method is preferred as the initial step for MPI because it can be implemented as a fully data-driven pre-stack domain approach in either forward data space or inverse data space. In all cases, the MPI scheme generates internal multiple models with improved kinematic and dynamic accuracy.

Recent sediments forming Scolt Head Island have been divided into beach, dune and tidal inlet environments on physiographic and sedimentological criterion. A technique of particle, analysis, based on the Emery Settling Tube, has been developed to investigate grain-size characteristics. It was found impossible to distinguish the different environments by this property alone. A theory of fractionation has been proposed to interpret the general grain-size trends shown by these sediments. An attempt has been made to relate the sediments to the existing dynamic (wave and current) conditions controlling their deposition. The theoretical wave activity on the Scolt Head Island beach has been calculated from meteorological data. A residual westward longshore component of wave action has been determined. The tidal range has been shown to cause an increase in wave action on the beach as the tide rises. This causes an increase in both the grain-size of the beach material, and of the beach slope, from the low to the high water level. Current action along the front of Scolt Head Island is believed to produce an eastward residual sediment transport in the near-shore zone. This is balanced by the residual westward longshore drift of the fine grained sand on the lower part of the beach. Direct current measurements have been related to the sediment carried in suspension in Brancaster Harbour which separates Scolt Head Island from the mainland. The grain-size distribution of certain sand deposits in the inlet have been related to the local current pattern. A comparison between a series of Ordnance Survey maps indicates that Scolt Head Island has, during historical time, migrated shorewards and grown by accretion at its western end. Its shorewards migration results from coastal erosion caused by the post glacial rise in sea level; while the accretion at its western end reflects the dominant westward littoral drift, as well as (indirectly) the erosion of the Burnham Bank Complex lying to the north of the north Norfolk coast. The evolution of this bank complex has been studied by comparing a series of Admiralty charts. Changes in its topography have been related to the tidal current pattern. This indicates that a. closed circulation, based upon the directions of the strongest currents (and, therefore, of residual sediment movement), causes sediment to be deposited. Erosion occurs where a closed circulation is absent.

A region surrounding a cumulus cloud is defined in such a way that (when virtual temperature effects are neglected) there is no sensible heat transfer across the boundaries of the region. This simplifies the discussion of the interaction between the cumulus and its environment. A model of the region, which is called the white box, is developed and an estimate is made of the net vertical mass transport within it as a function of height. Rain and cloud radiation have the effect of modifying this transport and may be described in terms of it. If the requirements of continuity are satisfied by means of an alteration in the downstream direction of the wind profile of the environment, the wind near the base of the cloud is increased downstream. It is shown that cumulus convection can destabilize as well as stabilize its environment. A two-dimensional steady-state model of the atmosphere in the presence of the white box is developed and applied to trade-wind data. The resulting profile of mean vertical velocities in the white box bears out the predictions made earlier. It is found that the geostrophic assumption is inconsistent with the presence of the cumulus cloud. The results of this work suggest that cumulus convection bears no analogy to Benard convection.

This Thesis describes an investigation of the geological causes and influences affecting the existence of linear features seen on air photographs of areas where the bedrock is obscured by superficial deposits. Detailed stereoscopic studies were made of the appearance of these features, and their causes were then investigated in the field. During the fieldwork all the factors considered likely to influence their existence were recorded, and similar data were recorded where important linear geological occurrences had not been detected as linear features on the air photographs. The results were then studied in an attempt to find a relationship between the appearance of a linear feature and its cause, and also to discover factors that inhibit the detection of important geological data on air photographs. The linear features selected were found to include nine tenths of the boundaries of different types of superficial deposits, three quarters of all the buried faults and three quarters of the buried rock contacts. Half the remaining soil boundaries, faults and rock contacts also showed as less distinct features on the photographs. Further information on the state of the hidden bedrock was shown by other linear features that were caused by bedding planes, joints, surface gullys, fracture zones and dykes. Some natural linear features originated within the superficial cover, such as those caused by landslides, glacial effects, old coastlines and man—made features. Each type of geological phenomena tended to have a varied appearance in different settings, and a series of characteristics were studied for each linear feature so that a variety of interpretation criteria were secured to give a photogeologist as sound a basis as possible on which to make decisions.

At the present time massive stratiform sulphide deposits are widely regarded as having an exhalative-sedimentary origin. The applicability of this view to the Rio Tinto deposits has been tested by investigating whether or not there is evidence in the essentially pyritic San Dionisio ore body of the regional metamorphic and tectonic activity. The stratigraphic conformity and the shape of the lode suggest that its present configuration may have been derived by folding during the first phase of deformation which affected the volcanic and sedimentary country rocks. The granular structure of the massive ore has been systematised by distinguishing several microstructural assemblages. Almost every type of microstructure is characterised by the presence of euhedral compositional zoning in the component pyrite grains. By examining possible modes of recrystallisation in the natural environment it has been shown that the zoning is not a metamorphic feature, but records the transient grain shapes during the primary depositional history of the lode. The main grain size and shape characteristics of the pyrite aggregates are defined independently by zone structures and represent primary growth fabrics which were not deteotably modified by recrystallisation. The instability of the compositional zoning under metamorphic conditions permitting volume diffusion in the pyrite lattice was demonstrated in a series of week-long experiments in which the natural ore was recrystallised in the solid state at temperatures between 600°C and 700°C. From the morphology of the lode contacts and of internal primary marker surfaces it is argued that if the lode has been folded there should be evidence of observable displacements spaced at distances in the order of a few grain diameters or less. Except for fine grained pyrite ellipses, which originated from amorphous spherical precipitates and were distorted in a non-crystalline state, there is no record in the micro-structure of the ore that the initial growth fabrics were deformed during the regional folding. Primary growth structures in the pyrite aggregates are shown to have retained their original forms, and the structure, distribution and arrangement of primary intragranular zones is found to be inconsistent with the predicted effects of cataclastic deformation and mechanical and diffusional plastic deformation. Slickensides were apparently produced during an elastic deformation involving cyclic movements along isolated fracture planes. Friable zones of ore along the axis of the main syncline are re-interpreted in terms of leaching activity for which there is also considerable evidence in the microstructure of the pyrite aggregates.

The sub-aerial basement shield of Tenerife is comprised largely of basanites, ankaramites, and rarer oceanites. Near the centre of the island, in the area now termed Las Canadas, extensive intermediate and salic volcanism followed the shield building stage,producing the Vilaflor volcanic complex. Detailed mapping indicates that the Vilaflor volcanics were erupted from a series of poorly defined centres lying along an east-west fissure, one of two or possibly three fissures that have dominated the major sub-aerial volcanic history of Tenerife. In the major growth period of the Vilaflor complex, traehybasanite, plagioclase phonolite, and phnnolite flows were erupted, along with phonolitic pumice lapilli,s coria, and an ash flow. Following this the final growth period represents a restriction of volcanism to local centres, phonolites were the dominant rock type and viscous flows, thick pumice lapilli and abundant volcanoclastic deposits were formed. A major collapse along the length of the complex completely removed the northern part and some of the southern part of the complex,leaving two depressions,bounded southward by two curved escarpments, the Portillo escarpmen in the east,and the Tauce escarpment in the west. Comparison of the escarpments with the Orotave and Guimar valleys on Tenerife, El Golfo on Hierro, and La Taburiente caldera on La Palma, indicates that landsliding, in conjunction with magmatic processes has produced all these features. Post-collapse activity north of the escarpments has built up the twin volcanoes of Viejo and Teide, both displaying central and flank vent activity. Viejo is surmounted by a dormant caldera, whilst Teide displays weak fumerole activity from the top cone, El Piton, and from an arcuate region on the southern flanks.The Viejo flows are trachybasanites, rarer plagioclase phonolites and late, viscous phonolites. The Teide volcanics are entirely phonolitic. Chemically the rocks are divided into basanites, trachybasanites, plagioclase phonolites, and phonolites, they are all strongly alkaline, and most are strongly undersaturated. High-alumina trachybasanites are very common whilst the phonolites are very variable in degree of undersaturation,and minor element geochemistry. The suite is thought to be formed by crystal fractionation from a basanite parent.