Ondes de surface

Résumé Le but de ce mémoire est de démontrer quelques nouvelles propriétés générales d'une classe de fonctions (les ondes de surface) très importante par son rôle en physique et en géophysique.On commence par la démontration d'un théoréme fondamental qui établit l'identité de l'ensemble des ondes de surface et de l'ensemble des fonctions pour lesquelles, à tout instantt ₀ et en tout pointA ₀ de leur domaine d'existence, on peut écrire une proportionnalité entre intervalles de temps (situés, en général asymétriquement, de part et d'autre det ₀) et rayons des domaines circulaires centrés enA ₀, telle que les moyennes temporelles et spatiales correspondantes soient égales. Ce théorème permet d'écrire, en termes finis, la solution des équations aux dérivées partielles de toute onde de surface.On applique ensuite les résultats généraux: 1° à la variation diurne de la pression lce qui permet de voir que ce phénomène peut être considéré comme une onde de surface et donne la loi fondamentale en cos³ ( latitude) pour l'amplitude de l'onde semidiurne progressive]; 2° aux ondes de variation de la pression synoptique. Pour ces ondes de variation on établit les relations qui existent entre leurs paramètres caractéristiques et on détermine finalement leur configuration théorique.

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Summary The aim of this paper is to give the proof of some new general properties of a class of functions (the surface waves) which is very important in physics and geophysics.We first give the proof of a fundamental theorem establishing the identity of the set of all surface waves and the set of functions for which, at any momentt ₀ and at any pointA ₀ of their domain, there exists a proportionality between time intervals comprisingt ₀ (asymmetrically, in the general case) and the radius of the circular domains centered onA ₀, such that the corresponding temporal and spatial means are equal. This theorem allows to write in finite terms the solution of the partial differential equations of any surface wave.The general results are then applied: 1° to the diurnal pressure variation, showing that this phenomenon can be considered as a surface wave and giving the fundamental law cos³ ( latitude) for the amplitude of the progressive or travelling 12-hourly wave; 2° to the waves of the synoptic pressure variations. For these waves the relations between their characteristic parameters is first established and finally their theoretical spatial configuration or pattern is deduced.

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Communication faite le 23 Avril 1957 à la Cinquième Assemblée de la «Società Italiana di Geofisica e Meteorologia» (Genova, 23–25 Avril 1957).     

Single-particle crushing strength under different relative humidity conditions

This paper presents a fundamental study on the effect of the relative humidity on the rockfill crushing strength. This aspect plays an important role in the mechanical behaviour of rockfill, and it is known that certain characteristics of the granular materials, such as compressibility and shear strength, depend on the confining stress, which is a function of the particles crushing. An increased interest has been observed regarding the effect of the relative humidity in the mechanical behaviour of rockfill. Unfortunately, limited research has been conducted until now regarding the study of individual particle crushing. Therefore, this paper thoroughly investigated particle crushing, by performing single-particle crushing tests on rockfill particles divided into four size ranges, under different relative humidity conditions. The experimental results reveal a considerable influence of the relative humidity in the studied rockfill particles, whose strength of the particles with the greatest dimensions in saturated conditions was reduced by half. Consistent macro-mechanical evidence demonstrates that particle’s size and relative humidity conditions depict the most important factors that influence particle crushing strength.

     

The electrical conductivity of Posidonia black shales — from magnetotelluric exploration to rock samples

We carried out a magnetotelluric field campaign in the South–East Lower Saxony Basin, Germany, with the main goal of testing this method for imaging regional Posidonia black shale sediments. Two‐dimensional inversion results of the magnetotelluric data show a series of conductive structures correlating with brine‐saturated sediments but also with deeper, anthracitic Westphalian/Namurian coals. None of these structures can be directly related with the Posidonia black shale, which appears to be generally resistive and therefore difficult to resolve with the magnetotelluric method. This assumption is supported by measurements of electrical resistivity on a set of Posidonia shale samples from the Hils syncline in the Lower Saxony basin. These rock samples were collected in shallow boreholes and show immature (0.53% Ro), oil (0.88% Ro), and gas (1.45% Ro) window thermal maturities. None of the black shale samples showed low electrical resistivity, particularly those with oil window maturity show resistivity exceeding 10⁴ Ωm. Moreover, we could not observe a direct correlation between maturity and electrical resistivity; the Harderode samples showed the highest resistivity, whereas the Haddessen samples showed the lowest. A similar trend has been seen for coals in different states of thermal maturation. Saturation of the samples with distilled and saline water solutions led to decreasing electrical resistivity. Moreover, a positive correlation of electrical resistivity with porosity is observed for the Wickensen and Harderode samples, which suggests that the electrical resistivity of the Posidonia black shale is mainly controlled by porosity.     

The European Marine Strategy: Contribution and challenges from a Portuguese perspective

The EU Marine Strategy Framework Directive (MSFD) is considered to be the environmental pillar of the EU Integrated Maritime Policy, establishing a framework within which member states must take the necessary measures to achieve, or maintain, good environmental status in their marine waters. This study presents Portugal's contributions to the Directive development, describes the Portuguese institutional framework within the MSFD and, finally, highlights the opportunities and threats to the success of the MSFD implementation in Portugal. The latter entails an analysis of the Directive's long term adequacy in its link to (1) marine spatial planning, (2) climate change and (3) the economic/financial crisis. With one of Europe's largest exclusive economic zones. Portugal's interest in the MSFD is paramount. Efforts towards the approval of the final document were assured during the Portuguese presidency of the European Council of Ministers, in 2007, while chairing a thorough discussion between the Council and the European Parliament. In the Portuguese context, the Directive implementation will rely on the Water Institute as the authoritative entity, which will be responsible for coordinating all necessary efforts at the national level. The success of such process depends on a close cooperation among the institutions involved as well as on how approved measures account for long term issues. In addition, the MSFD implementation must be built on lessons learned within the Water Framework Directive, in order to be successful. Although it poses a methodological challenge to Portugal, the MSFD implementation is expected to contribute significantly to the improvement of coastal/marine conservation and management at the national level.     

Tsunami vulnerability assessment of Casablanca-Morocco using numerical modelling and GIS tools

Earthquakes and tsunamis along Morocco’s coasts have been reported since historical times. The threat posed by tsunamis must be included in coastal risk studies. This study focuses on the tsunami impact and vulnerability assessment of the Casablanca harbour and surrounding area using a combination of tsunami inundation numerical modelling, field survey data and geographic information system. The tsunami scenario used here is compatible with the 1755 Lisbon event that we considered to be the worst case tsunami scenario. Hydrodynamic modelling was performed with an adapted version of the Cornell Multigrid Coupled Tsunami Model from Cornell University. The simulation covers the eastern domain of the Azores-Gibraltar fracture zone corresponding to the largest tsunamigenic area in the North Atlantic. The proposed vulnerability model attempts to provide an insight into the tsunami vulnerability of building stock. Results in the form of a vulnerability map will be useful for decision makers and local authorities in preventing the community resiliency for tsunami hazards.     

Runoff from soils under different management and simulated rainfall regimes in southern Brazil

Abstract

Surface runoff and drainage were evaluated for southern Brazilian soils subjected to different rainfall intensities and management practices. Soils received up to four applications of simulated rainfall in sequences with one application per day. Seven lysimeters, each of 1 m³ volume, were used to measure drainage volume, with measurement of initial and final water content, times at which surface runoff and lysimeter drainage began, and the volume rates of flow. At the end of the second test, soils were subjected to two levels of disturbance (denoted by low and high soil movement) by opening furrows. These cultivation treatments altered the times at which lysimeter surface runoff and drainage were initiated, the rates of surface runoff, the final infiltration and internal drainage, and the components of the water balance throughout the series of trials. Mean times at which surface runoff was initiated in lysimeters subjected to greater soil disturbance were longer than those with little soil disturbance. Final infiltration rates were greater in lysimeters with little soil disturbance. It was also found that lysimeter surface runoff generation was influenced by the state of development of maize grown in the lysimeter.

Editor D. Koutsoyiannis; Associate editor G. Mahé     

The role of porosity in the development of authigenic dolomite and palygorskite. An example in siliceous sandstones of continental origin in Western Spain

During the Tertiary, the Hercynian basement of the Iberian Peninsula was uneven due to Alpine tectonism which led to the development of a set of horsts and grabens forming its main geological structure. One of these grabens is the Ciudad Rodrigo Basin, located close to the Portuguese border. The south-western margin of this graben is filled with arkosic sandstones of continental origin that, once deposited, underwent important low-grade diagenetic processes related to the surface processes. The main diagenetic processes were hydrolysis, replacement by carbonate, and argillization to palygorskite. These three processes led to the differentiation of three main levels within the outcrops studied: (1) the Lower Level, where the original clayey sandstone outcrops, displaying fairly hydromorphic traits; (2) the Middle Level, where part of the clayey matrix has been replaced by dolomitic carbonate; and (3) the Upper Level, where palygorskite is the new neoformed clay. The change in porosity seems to have been the controlling factor, since it governs the dynamics of the solutions inside the rocks. These conditions changed from being diffusion-driven, at the start of the diagenesis, to flow-driven as porosity increased.     

Aquifer development planning to supply a seaside resort: a case study in Goa,India

Using the hydrogeological and socio-economic data derived from a European Commission research project on the measurement, monitoring and sustainability of the coastal environment, two optimization models have been applied to satisfy the future water resources needs of the coastal zone of Bardez in Goa, India. The number of tourists visiting Goa since the 1970s has risen considerably, and roughly a third of them go to Bardez taluka, prompting growth in the tourist-related infrastructure in the region. The optimization models are non-linear mixed integer models that have been solved using GAMS/DICOPT++ commercial software. Optimization models were used, firstly, to indicate the most suitable zones for building seaside resorts and wells to supply the tourist industry with an adequate amount of water, and secondly, to indicate the best location for wells to adequately supply pre-existing hotels. The models presented will help to define the optimal locations for the wells and the hydraulic infrastructures needed to satisfy demand at minimum cost, taking into account environmental constraints such as the risk of saline intrusion.

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Résumé A l’aide de données hydrogéologiques et socio-économiques, dérivées d’un projet de recherche de la Commission Européenne sur l’étude, la surveillance et la durabilité de l’environnement c?tier, deux modèles d’optimisation ont été appliqués en vue de satisfaire les besoins futurs en ressources en eau de la zone c?tière de Bardez au Goa en Inde. Le nombre de touristes qui visitent le Goa depuis les années 70 a considérablement augmenté et environ un tiers d’entre eux se rend à Bardez taluka, ce qui encourage la croissance des infrastructures liées au tourisme dans la région. Les modèles d’optimisation sont des modèles non linéaires mixtes en nombres entiers qui ont été résolus en utilisant le logiciel commercial GAMS/DICOPT++. Les modèles d’optimisation ont été utilisés pour indiquer premièrement les zones les plus appropriées pour construire des stations balnéaires et des puits pour approvisionner en quantité d’eau suffisante l’industrie touristique, et deuxièmement pour indiquer la meilleure localisation de puits pour l’alimentation des h?tels préexistants. Les modèles présentés aideront à définir les localisations optimales des puits et des infrastructures hydrauliques nécessaires à la satisfaction de la demande à un co?t minimum, tout en prenant en compte les contraintes environnementales, tel que le risque d’intrusion saline.

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Resumen Se han aplicado dos modelos de optimización en base a datos socio-económicos e hidrogeológicos derivados de un proyecto de investigación de la Comisión Europea sobre medición, monitoreo y sostenibilidad del ambiente costero para satisfacer las necesidades futuras de recursos hídricos de la zona costera de Bardez en Goa, India. El número de turistas que visita Goa desde la década de 1970′s ha subido considerablemente y cerca de un tercio de ellos van a Bardez taluka impulsando el crecimiento en la infraestructura turística de la región. Los modelos de optimización son modelos de números enteros mixtos no-lineales que se han resuelto usando el programa comercial GAMS/DICOPT++. Los modelos de optimización se usaron, primero para indicar las zonas más adecuadas para la construcción de centros de diversión en las márgenes del océano y pozos para abastecer la industria turística con una adecuada cantidad de agua, y segundo, para indicar la mejor localización de pozos para el abastecimiento de hoteles pre-existentes. Los modelos que se presentan ayudarán a definir las localizaciones óptimas para los pozos y las infraestructuras hidráulicas necesarias para satisfacer la demanda al mínimo costo, tomando en consideración restricciones ambientales tal como el riesgo de intrusión salina.