En contexte insulaire volcanique, les aquifères du domaine côtier présentent de très fortes hétérogénéités liées à leur structure, à la disparité de leurs recharges et à l'influence des conditions en aval. Les travaux envisagés ici consistent à élaborer une méthodologie adaptée à différentes configurations hydrogéologiques dans l'optique de mieux imager et comprendre l'évolution du biseau salé. L'acquisition des données est effectuée sur différents sites présentant des configurations hydrogéologiques variées sur le plan de la recharge, de la structure de l'aquifère et de la géomorphologie de la limite en aval. Un réseau d'observation est mis en place sur la côte ouest de l'île de La Réunion, dans la zone littorale allant de L'Ermitage à Saint-Leu. Cette zone est particulièrement intéressante dans le sens où elle présente les types de limites en aval les plus communes aux îles volcaniques à savoir, des côtes rocheuses, des plaines d'arrière-récif et des plaines d'accumulation fluviomarine. Sur La Réunion et la Grande Comore, le milieu volcanique est investigué au moyen de méthodes géophysiques et par une analyse de séries temporelles hydrogéologiques. Les outils géophysiques employés confirment la présence d’un milieu souterrain hétérogène, avec la présence sporadique de chenaux d'écoulement souterrain préférentiel susceptibles de contrôler la dynamique des intrusions marines. Les simulations numériques effectuées par la suite corroborent ces observations. L'analyse des signaux enregistrés indique une forte influence des forçages hydro-climatiques externes sur les nappes côtières. Elle permet aussi de distinguer deux familles de comportement selon le contexte géologique des ouvrages instrumentés. Les résultats de ces travaux mettent en avant une méthodologie de gestion des nappes côtières adaptée au milieu volcanique. Ils contribuent également à l'orientation des programmes de prospection de la ressource en eau souterraine dans ces contextes très complexes. / In volcanic islands context, the aquifers of coastal areas have very strong heterogeneities related to their structure, the disparity of their recharge and the influence of the downstream boundaries (rocky coasts, detritic cones...). The works considered here consist to develop a methodology adapted to different hydrogeological configurations in the aim to better understanding the development of saltwater intrusions. Time series recording and geophysical investigations are carried out on various sites, with different hydrogeological conditions, on the west coast of Reunion Island and throughout Grande Comore Island. The groundwater observatory tested in the pilot study area of Reunion was exported to three others experimental sites situated in Grande Comore Island (Indian Ocean). The geophysical investigations reveal a very important lateral heterogeneity along the shoreline due to the existence of 3D volcanic structures such as palaeovalleys filled by recent lava flows. In coastal areas, these structures exert an important role towards the marine intrusion dynamics, like it was confirmed by numerical simulations. Time series recording has allowed the hydrodynamic characterisation of the coastal groundwater and has enhanced the understanding of low and high frequency variations of the groundwater resources quality

This study is part of an NRF sponsored research project entitled “Neotectonics and its applications for the exploration of groundwater in the fractured Karoo aquifers in the Eastern Cape” under the NRF Niche area of Water Resources Management and Sustainable Development in the Eastern Cape Province. The identification of relatively highly productive wells in the Karoo fractured aquifers is extremely difficult. This study aims to identify neotectonic zones and lower stress fields, and apply the results to groundwater exploration in the Eastern Cape Province. The methodologies adopted in this study include: a comprehensive literature review, extensive field mapping and investigation such as road cuts, sampling for laboratory studies, examination of seismic data, study of hot and ordinary springs, and interpretation of aerial photography and satellite images. Three main neotectonic belts were identified in the Eastern Cape (southern neotectonic belt, northern neotectonic belt and eastern neotectonic belt) based on literature review and field interpretations. The southern neotectonic belt (from the Cape Fold Belt to the lower Beaufort Group boundary) is characterized by the reactivation of the Coega-Bavianskloof and Sauer faults, the presence of a hot spring near Fort Beaufort, the slickenlines and discrete slickenlines and specifically the seismic events that were recorded in the Eastern Cape from 1850 to 2007. In this southern neotectonic belt the remote sensing has also revealed the presence of the Fort Beaufort fracture, the quartz veins seen in some dolerites and the different vegetation types along it may indicate that this fracture is possibly a fault; moreover the Quaternary sediments and weathered dolerites indicate that the Fort iii Beaufort fracture is characterized by groundwater circulation and accordingly is a good target for groundwater exploration, this fracture is a post-Karoo structure and possibly a neotectonic feature. In addition, the kaolin deposit, chiefly developed in the Dwyka tillite near Grahamstown is clearly controlled by neotectonic fracture zones. The northern neotectonic belt near the country of Lesotho is marked by the presence of the Senqu seismotectonic regime and hot springs. The Quaternary Amatole-Swaziland (formerly Ciskei-Swaziland) axis of uplift makes the eastern part of the province the third neotectonic zone, the asymmetric meanders of the Mbashe river in the vicinity of Qunu near Mthatha derived possibly from this Quaternary uplift; this asymmetric feature of meanders implies that the river has tried to maintain stability of its valley where tilting occurred. Within these neotectonic belts the central part of the Eastern Cape may be considered a static and inactive belt. A northwesterly trend for the maximum principal compresssional stress predominates in the Eastern Cape and is correlated with the present major structural control of the province. The current stress regime determination was derived from faults, joints and quartz veins only on kaolin deposits. Systematic joints reflect regional tectonic stress trajectories at the time of fracturing. Discharge rates of groundwater from boreholes as provided by the Department of Water and Forestry were used to confirm and predict water exploration targets. The region of Tabankulu (near Kwazulu Natal) in the northern neotectonic belt has remarkable discharge rates of groundwater (11.1 l/s, 4.65 l/s, 6.49 l/s, 42 l/s). The region of Mthatha, nearly surrounding the Amatole-Swaziland axis (former Ciskei-Swaziland iv axis) of uplift which might have generated some new faults, has a number of springs. These two regions should serve as case studies for future research. Apart from these two regions, two others regions can be considered as case studies for future groundwater exploration targets: the Bath Farm hot spring near the Fort Beaufort neotectonic fault and the vicinity of what is known as the Fort Beaufort fracture near Teba and Cimezile villages 20km north west of Fort Beaufort. It is concluded that the study of neotectonics and stress fields may be a useful tool for groundwater exploration in the Karoo fractured aquifers in the Eastern Cape, and in similar regions elsewhere in South Africa and in Africa.

Les outils de la géodésie spatiale sont aujourd'hui très fortement impliqués dans les études géophysiques. Le champ de déformations horizontales d'un site d'étude est fourni par les vecteurs déplacement ou par un champ tensoriel. Ce dernier possède l'avantage d'être indépendant de tout référentiel, contrairement à ce qui est nécessaire pour exprimer les vecteurs vitesse. Néanmoins, les méthodes de calcul de tenseurs dépendent souvent d'une décomposition arbitraire en figures élémentaires à partir des points de mesures géodésiques. De plus, la représentation de ces tenseurs selon leurs axes principaux est d'une lecture et d'une interprétation assez difficiles et nécessitent un certain entraînement. Cette thèse traite, dans un premier temps, le problème de fournir un champ continu de déformations sous la forme des tenseurs régulièrement répartis, de façon peu dépendante des points de mesure, et dans un deuxième temps, de fournir une représentation cartographique intuitive de ces tenseurs avec, pour la première fois, une représentation simultanée de leur degré de significativité. L'estimation des incertitudes de la déformation obtenue est analysée selon deux points de vue : d'une part, une méthode de Monte Carlo est appliquée pour la détermination des barres d'erreurs liées aux mesures, son résultat permet le calcul de degré de significativité des tenseurs par comparaison des valeurs de tenseurs par rapport à leurs incertitudes, et d'autre part, une estimation des contraintes imposées par la géométrie de distribution des points de mesures qui est ensuite combinée avec la première source d'erreur. La nouvelle approche de représentation a été analysée via une enquête auprès d'un groupe de géophysiciens, en leur fournissant plusieurs possibilités de représentations. En se basant sur les résultats de cette enquête, nous avons pu valider la nouvelle représentation qui permet de mettre en évidence certains aspects mal mis en évidence par la représentation classique, et donc le choix des éléments graphiques de la carte permettant de fournir la représentation la plus intuitive possible / Space geodesy tools are now strongly involved in geophysical studies. The horizontal deformation field for a region of interest is provided by two main methods : a velocity field and a strain tensor field. A strain tensors field solution has the advantage of being independent of the reference frame in which the velocities are expressed. Nevertheless, the current methods of calculation of a strain tensors field depend on the positioning of geodetic points. Furthermore, the current mapping method of tensors by their mains axis is not easy to read and to interpret, needing some training. This thesis is devoted to the problem of calculating a continuous field of regularly spaced strain tensors, and providing an intuitive mapping method of these tensors with a simultaneous representation of their significance level on the same map. The estimation of uncertainties related to the deformation field is made in two steps : firstly, a Monte Carlo method is applied for the calculation of uncertainties related to the measurements, its results allow to define the significance level of tensors by normalizing tensor's values with respect to their related uncertainties, then, the constraints coming from the distribution of the network of measurement points are calculated and combined with the first source of error. The new approach of mapping tensors was analyzed through an opinion survey by providing several possibilities of representation. The results of this opinion survey allowed us to validate this new mapping method by geophysicists for representing a deformation field, because it allows highlighting some aspects not well illustrated by the classical mapping method of tensors, and therefore choosing the graphical elements of the map which provide the best intuitive method of mapping a strain tensors field

MESHWR / Department of Hydrology and Water Resources / See the attached abstract below

Master's thesis deals with the micro-region Klánovice's forest and its surroundings on the eastern edge of the City Prague. This area has not been given comprehensive attention yet. The findings are based on a critical review of the humble written and archaeological sources relating to the concerned area. In addition, was made, analysis of archaeological excavation, which was carried out on the deserted village Hol and also geophysical survey from the same site. Based on the lessons learned to better classify and discuss the role of this area in the hinterland of high medieval Prague. Keywords: deserted village, Klánovice forest, Hol, geophysical survey, ceramics, agricultural margins land, high middle ages

The physical properties of the coarse fraction of the till (0.4 to 20 cm) and the surface boulders have been studied at two different sites in Sweden. The research work included: development of a new image analysis software for 3D size and shape measurements of particles; lithological analysis on multiple size fractions in till and magnetic susceptibility survey on coarse till clasts, surface boulders and local bedrock. The new 3D image analysis method provides an enormous amount of size and shape data for each particle in the coarse fraction (2 to 20 cm) in till. The method is suitable for field study, cost effective and the software is executable in Matlab. The field imaging method together with the image analysis software give non subjective results of size and shape of coarse particles and makes it feasible and easy to study representative sample size, which is one tonne for testing clasts of size up to 20 cm. The lithological analysis of the multiple size fraction of the till clasts has been investigated on six different size fractions of the till (0.4 to 20 cm); the result of the different samples from the two sites shows that this method can potentially be used as a stratigraphic tool in the areas where there is no unique indicator lithologies. The magnetic susceptibility has been made on the surface boulders, the 6-20 cm till fraction and on insitu bedrock outcrops near to the study sites. The method has good potential for determining stratigraphic relationships between different till units as well as for determining the provenance ofcoarse clasts and surface boulders. / QC 20110413

No description available.

A computer technique for interpreting geophysical logs of drill-holes in quantitative lithologic terms has been developed and tested on the deposits of the late Eocene Coaledo Formation, a well-studied fluvio-deltaic complex in southwestern Oregon. The technique involves the use of induced and natural gamma logs for separation of coal and claystone from coarse-grained detrital rocks and the use of the ratio of resistivity and natural gamma responses (defined here as the "grain size index") to divide the coarse elastic rocks into a series of textural classes corresponding to the Wentworth-Odden particle size scale.

No description available.

No description available.