In 1939, Spyridon Marinatos advocated in the archaeological journal Antiquity that the Bronze Age Santorini eruption directly caused the destruction of the Minoan civilisation on Crete. Since then, the study of this eruption has been carried forward by countless researchers inspiring three international conferences, the proceedings of which have provided a valuable source of information on the Archaeology and Volcanology of the eruption. Despite the eruption's popularity in the academic and mainstream literature, there still remain several aspects that have been previously under-researched. In the context of a critical examination of tephra dispersal modelling methods, eruption deposits and observations and interpretations of field data, this thesis has sought to shed light on some of these. Volcanic ballistics have been used to obtain first-order estimates of velocities and eruption overpressures for ballistics landing at the archaeological site of Akrotiri. This is the first known study to contribute a solely quantitative ballistic investigation into the interaction between the eruption products and Akrotiri. A forward model has been used in conjunction with two inversion methods to take a unique approach to clarify source conditions and transport parameters of the eruption. Reconstructions of the eruption conditions and seasonality have been made that are consistent with the resultant deposit patterns. Observations of pyroclastic mud flow emplacement on shallow slopes outside the caldera walls can only be consistent with the caldera being infilled with eruption products that are not preserved. Field observations and seismic reflection surveys suggest this material was downfaulted. This novel hypothesis is developed and tested, and the eruption volume re-estimated to include this additional material. Finally, the stratigraphic relations of Santorini's intracaldera fill are examined and a new volcanological interpretation of the deposits is presented. The downfaulted material is suggested to be made up of six characteristic layers, the volumes of which have been used to calculate the rate of volcanism and magma supply since the Minoan eruption. 11

The Bird's Head area of New Guinea is underlain by Australian continental crust and has a relatively complete Palaeozoic to Recent stratigraphic record . There are a number of siliciclastic dominated formations which include the Mesozoic Tipuma Formation and the Cenozoic Sirga, Klasafet, Klasaman. and Steenkool Formations. The aim of this study was to investigate their provenance, date them better, and interpret their significance for the history of New Guinea. New fieldwork was carried out, complemented by analysis of light and heavy minerals, X-ray diffraction of clay minerals, U-Pb zircon geochronology, and quartz CL luminescence study. The Tipuma Formation was previously dated only by its stratigraphic position and was suggested to have been deposited in a continental passive margin. This study shows sands tones and conglomerates were sourced from acid volcanic, metamorphic, and recycled sedimentary rocks to the north of the formation, and from the North Australian Craton. The youngest zircon ages indicate it was deposited in the Triassic. It records long-lived Palaeozoic volcanic activity interpreted to indicate subduction of the palaeo-Pacific oceanic plate under the Australian continent associated with an Andean-type active margin that followed the Tasman Line. It is suggested that the Tasman Line continued from eastern Australia, through New Guinea, into the Bird's Head region which was part of Australia since at least the Triassic. The Oligocene-Miocene Sirga Formation was previously interpreted as related to collision of New Guinea with Pacific are terranes but there is no evidence of arc-derived material in Sirga Formation sandstones. Some quartz-rich sandstones mapped as Sirga Formation contain Pliocene zircons. The Upper Neogene siliciclastic rocks of the Bird's Head were deposited in an extensive flood plain to a shallow-marine environment. All contain evidence of acid magmatism. They were also sourced from volcanic or hypabyssal equivalents of Upper Carboniferous to Triassic intrusive bodies , older sedimentary rocks, and the Kemum Formation. 3

No description available.

Subglacial explosive volcanism generates hazards resulting from magma-ice interaction, including meltwater flooding and fine-grained volcanic ash. The literature contains descriptions of some recent subglacial eruptions and suggests several heat transfer mechanisms but lacks a detailed study of heat transfer in the magma-water-ice system. Quantification of heat transfer processes allows further development of dynamic models of subglacial eruptions that may help to inform hazard management. 1 have quantified particle-water heat transfer with a model that couples intraparticle conduction with boiling on particle surfaces. In general, where magma is fragmented by explosion or granulation, much of the initial heat of the magma is transferred to water rapidly compared to eruption timescales. Within liquid-dominated subglacial eruption cavities, heat fluxes from water to ice of c. 0.6 MW m-2 can be obtained by single phase free convection. When local boiling occurs in the vent region heat fluxes of 3-5 MW m-2 , approaching those inferred for some recent subglacial eruptions, may be attained by two-phase free convection and may be increased by momentum transfer from the eruption jet. In vapour-dominated cavities, heat fluxes of 0.1-1 MW m-2 can be obtained by steam condensation during free convection, depending on cavity pressure and the concentration of non-condensable gases present. Forced convection reduces the effect of non-condensable gases; in this case a maximum heat flux of c. 2 MW m-2 may be attained. In a drained and depressurised cavity the resulting eruption jet may transfer heat by a combination of radiation, steam condensation and pyroclast impact. Heat fluxes from radiation and condensation are unlikely to exceed 0.5 MW m-2. An experimental study of pyroclast impact on ice, using sand at 300 °C, demonstrated heat fluxes of 0.4 MW in-2. The effects of higher particle temperature and damage from repeated impact of larger particles remain to be investigated.

Explosive super-eruptions (≥450 km³) are amongst the most catastrophic events at the Earth's surface, with immediate and devastating regional environmental consequences. Recent catastrophic super-eruptions at Yellowstone are well-known, but the previous (Miocene) history of large explosive eruptions from the Yellowstone hotspot is less-well understood, even though some in the central Snake River Plain (cSRP) may have been similar in size, or larger. To test this, local successions of rhyolitic welded ignimbrites in the southern cSRP have been studied to distinguish and characterise individual eruption-units using a combination of fieldwork, whole-rock and mineral chemistry, rock magnetism and geochronology data to correlate them regionally. In the Rogerson Graben, the revised Rogerson Formation comprises five eruption-units, each designated as a member. In the Cassia Hills ~20 km further east, the revised Cassia Formation comprises thirteen eruptionunits, and a new deep drill-hole near Kimberly, reveals three rhyolitic eruption-units. Robust correlations between these sites and to the north of the Snake River Plain have revealed the presence of three new regionally widespread ignimbrite sheets: (1) the Brown’s View Ignimbrite (10.3±0.2 Ma; 2700 km²; 40 km³ DRE); (2) the McMullen Creek Ignimbrite (9.0 ±0.1 Ma; 12,000 km²; 589 km³ DRE); and (3) the Grey’s Landing Ignimbrite (~9.0 Ma; 18,000 km²; 708 km³ DRE).Using standard techniques to calculate eruption magnitudes, two of these record super-eruptions: the McMullen Creek eruption (magnitude 8.4, 1179 km3 DRE) and the Grey’s Landing eruption (magnitude 8.5, 1416 km³ DRE). These represent the largest super-eruptions within the cSRP and are also among the largest eruptions of the entire Snake River-Yellowstone volcanic province. The addition of the three correlations presented here has further reduced the total number of previously inferred eruption-units from 42 to 29. Therefore, mid-Miocene rhyolitic explosive eruptions in the central Snake River Plain were less numerous but significantly larger than previously thought.

Structural changes in active volcanic and producing geothermal systems are expected because of changes in the distribution of fluids, gases and cracks in the host rocks. Such changes have traditionally been studied using seismic tomography where two independent inversion results are differenced. A new tomography program tomo4d, inverts two epochs simultaneously, imposing constraints to minimize the structural differences calculated between different epochs. This method suppresses spurious changes not required by the data. Both methods were applied to data from Long Valley caldera and the Coso geothermal area, and the results compared. Long Valley caldera, California, has been seismically active since 1978. In particular, a region to the south of the resurgent dome (the “south moat”) and Mammoth Mountain have experienced multiple swarms involving hundreds of thousands of earthquakes. Inverting data from 1997 and 2009/10 using tomo4d detected changes with weaker anomaly strengths compared to those of simul2000A. Some changes imaged using simul2000A are thus not required by the data. Variable changes in Vp, Vs and Vp/Vs were detected and are interpreted as pore pressure decrease and/or drying of minerals, CO2 depletion and flooding during the tectonically active period. The Coso geothermal area, California, is highly seismogenic, with thousands of earthquakes occurring each year. Time-dependent seismic tomography was performed for the years 1996, 2006, 2007, 2008, 2010 and 2012 using both simul2000A and tomo4d. The epochs 1996-2006 and 2007-2012 were studied in detail. During the first epoch, Vp, Vs and Vp/Vs mostly increased in the geothermal field whereas during the second epoch changes were more varied and less extreme. It is concluded that different parts of this tripartite field have different reservoir characteristics, and that operational activities changed with time. These likely involved increasing water saturation in some areas as a result of increased water injection in recent years.

In recent years seismology has been used extensively to detect and locate the small scale (~10 km) structure of the Earth. In the mantle these structures likely represent chemical heterogeneity and are essential in our understanding of mechanical mixing processes within mantle convection. As subducted crust is chemically distinct from the background mantle, imaging the remains of the crust provides a tracer for convectional flow. In this study global and regional seismic heterogeneities in the mantle are found by processing teleseismic earthquake data through array seismology methods. Scattered energy from shallow earthquakes that arrives as PP precursors is studied in a 100 s quiet window before the main PP. Global average stacks of the PP wavefield are formed using data recorded at a global distribution of seismic arrays, for distances 70-120°. The resultant global stacks of PP have revealed that precursors to PP exist for all distances with the amplitudes increasing with distance and time. Regional stacks for the Pacific and Atlantic Oceans are found to contain very similar patterns of PP precursors suggesting scattering observed here does not vary with tectonic region. Global averages of PP precursors are modelled using a Monte Carlo phonon method that generates statistical scattering models for random media. Modelling results show that heterogeneities in the crust and mantle contribute to scattered PP wavefield. The best models found have 1% scattering strength in the crust, with reduced scattering strength of 0.8% in the uppermost mantle and an increase in scattering strength to 1% at ~700 km. Correlation length also varies from 2 km in the crust to 6 km in the mantle. The extent of the deeper mantle layer of heterogeneity is not well resolved and may be determined using larger epicentral distances. Regional patterns of heterogeneity are found from PP precursors that are scattered from small-scale heterogeneities in subduction zones. Array methods are applied to data in the epicentral distance range of 90°-110° from Eielson Array in Alaska, to calculate directivity and to enhance weak arrivals. Coherent precursors are selected automatically based on a semblance weighted beampower spectrum. Assuming single P-to-P scattering and using the directivity information from array processing, the origin of scattering is found by ray-tracing through a 1D velocity model. Most scatterers are imaged in western Pacific subduction zones with evidence for ~300 small-scale heterogeneities in the region around the present day Japan, Izu-Bonin, Mariana and West Philippine subduction zones. Most of the detected scatterers are located in the crust and upper mantle, but 6% are located deeper than 600 km. Scatterers in the transition zone correlate well with edges of fast features in tomographic images and subducted slab contours derived from slab seismicity. Deeper scatterers are located beneath the Izu-Bonin/Mariana subduction zones, which outline a steeply dipping pseudo-planar feature to 1480 km depth, and beneath the ancient (84-144 Ma) Indonesian subduction trench down to 1880 km depth. The cause of scattering is likely the underside reflection of the subducted Moho of subducted crustal material and are related to past and present subduction providing evidence that the subducted crust does descend into the lower mantle at least for these steeply dipping subduction zones. Combining the findings from both global and regional studies, it is likely that the heterogeneities detected in these studies are related to different stages of the mantle mixing cycle. As such a simple model for mid-mantle heterogeneity applicable to subduction zones has been suggested, with a well mixed mid-mantle of 6 km scale heterogeneities that have been thinned through mechanical stirring and a steeply dipping slab with attached crust penetrating to the lower mantle.

No description available.

Reservoir characterization refers to the process of inferring information about reservoir properties from seismic data. Obtaining accurate information about the reservoir properties such as porosity, lithology, and permeability is an essential objective in seismic exploration, especially in new areas that lack well control. This thesis contributes to the integrated analysis of 3-D seismic data and well logs for a square study area in the eastern province of Saudi Arabia, allowing improved understanding, interpretation and characterization of an upper Jurassic carbonate reservoir. The thesis focuses on the analysis aspect of the 3-D post-stack for seismic reservoir characterization through the interpretive use of seismic attributes using different approaches. The thesis can be divided into two key stages. First, a pre-processing stage covering the quality-control of the seismic data sets, calculation of seismic attributes, flattening of the 3-D seismic cube along target horizons, and calibration between seismic data and well-logs. The instantaneous attributes (amplitude, phase and frequency) of seismic data can be calculated and used, along with relative acoustic impedance, as the main seismic attributes to elucidate reservoir characteristics and to reduce exploration risk. Secondly, a main analysis stage develops and tests different effective techniques for analyzing seismic data and conducting reservoir characterization. Five main tools have been developed in-house through MATLAB coding to obtain accurate spatial mapping of the reservoir most important properties that can be used for modelling and simulation which provide better understanding of the reservoir under investigation. This particular choice of tools should work properly for post-stack data. The following summarises and highlights the main contributions of the thesis. First, is to enhance the predictive performance of the conventional multiple linear regression method through coupling information from cluster analysis. Then, I introduce the ‘grey system theory’, which was originally developed in China and has seen little application in geophysics, as a new tool for hydrocarbon exploration; I propose its use for detecting hydrocarbon anomalies associated with the carbonate reservoir. Next, I implement a Kohonen self-organizing map (SOM) neural network for clustering the reservoir heterogeneity (main lithofacies), and enhance the method by feeding it multiple attributes as an input. Furthermore, I estimate reservoir porosity and permeability by implementing a supervised back-propagation neural network. Finally, a hybrid approach that combines an artificial neural network and a fuzzy interface is developed for estimating well lithology from well logs. Different informative results were drawn from this study which can be summarised as follow: The result indicates that the upper part of the ZOI is more porous than the lower part. The reservoir porosity is ranging from 5% to around 28% within the ZOI with an average porosity of approximately 15%. In addition, the reservoir permeability shows ranging values from less than 500md to 2500md. The zone of interest (ZOI), in general, is divided into three distinct subzones ranging in their reservoir quality. This study indicates that the upper zone, middle zone, and lower zone of the ZOI are featured by (medium porosity / high permeability), (high porosity / low permeability), and (low porosity / medium permeability), respectively. The mapping result of the reservoir lithofacies spatial distribution indicates that there are at least nine major lithofacies deposits. Wackestone, packstone, grainstone, and mudstone are four types of the main lithofacies within the study area. The main conclusions drawn from this study can be summarised as follow: (a) The main aim of this study was achieved by estimating the reservoir porosity and permeability, as well as, clustering the reservoir lithology into the main lithofacies through ‘multiple linear regression’ and ‘artificial neural networks’ methods which proved (after validation) to be a powerful technique for characterizing reservoirs, especially the carbonate reservoir. (b) The grey system theory has been introduced to the reservoir study field and ‘grey attribute’ is proposed to highlight hydrocarbon accumulations after finding good correlation with the producing wells in the area. (c) An innovative implementation of ART2 neural network has been proposed to estimate the intra-well lithology by a hybrid-system that combines the neural network classification with the fuzzy interface for a better result. The final result indicated that the zone of interest (ZOI) is dominated by grainy packstone, wackestone/packstone, and muddy wackestone for the top, middle, and bottom subzones, respectively. Different regional maps have been generated for the reservoir main properties (porosity and permeability), lithofacies, and hydrocarbon accumulation. Validation of the result has been performed taken as a measure of the method performance and accuracy. The correlation coefficient was used to represent the success ratio. For example, the success ratio for predicting the reservoir porosity were 79% and 85% for the improved multiple linear regression method and back propagation neural network method, respectively. The result of each method has contributed substantially to achieve the main objectives of this study not only in obtaining better understanding of the reservoir spatial distribution for future planned drilling in the area, but also offering new input for remodelling the reservoir and updating the simulation.

Explosive magma-water interaction (MWI) during hydromagmatic eruptions generates substantially more fine-grained volcanic ash than equivalent 'dry' eruptions. However, the social and economic disruption caused by recent subglacial eruptions in Iceland highlighted gaps in our knowledge of the mechanisms responsible for fine fragmentation during MWI and the resulting implications for modelling ash dispersion. By developing new ways to characterise and interpret volcanic ash properties, this thesis shows that (a) magmatic vesiculation prior to MWI is the rule rather than the exception, (b) rapid quenching and brittle disintegration of vesicular melt (or pyroclasts) can explain the high fragmentation efficiency of hydromagmatic activity, and (c) the bubble population at the time of MWI is a fundamental control on the physical characteristics of the resulting pyroclasts. Covariation in the size, shape, and texture of hydromagmatic ash particles reflects interaction between the size distributions of particles and bubbles during brittle fragmentation, such that the length-scale and geometry of fracturing is controlled by the size and spatial distribution of bubbles. This result questions the validity of many of the 'diagnostic' particle properties used to distinguish magmatic from hydromagmatic deposits, and emphasises the need to analyse multiple grain size fractions to infer fragmentation mechanisms. I hypothesise that high thermal stress in glassy vesicular pyroclasts quenched during MWI is an important driver of secondary brittle fragmentation, a process that is compatible with, but not fully explored in, existing models of hydromagmatic processes. Importantly, the dynamics of vesiculation prior to MWI strongly influence the size and shape distributions of erupted material, both of which are critical input parameters for models of ash dispersion and resuspension