Potential and limits of double-difference tomographic methods

Double-difference tomographic methods use directly accurate time delays computed between similar signals. Such methods are designed to image very heterogeneous media, such as volcanoes or fault zones. In seismological applications, similar signals are recorded at a given station from earthquakes sharing similar and close-by sources. In seismic exploration experiments, similar signals are often recorded at neighbouring receivers. After a brief presentation of the tomographic algorithm used, a seismological application is summarized. The potential and limits of double-difference tomographic methods are explored using various numerical experiments. They show that two effects are competing in double-difference tomography: (i) the degradation of the stability of the inversion due to the geometrical proximity of the rays used in the differentiation and (ii) the decrease in modelling error, which allows improving the stability of the inversion and using smaller quantities of a priori information when data are sufficiently accurate. The best resolution is obtained for an optimal value of the inter-source or inter-receiver distance. For optimal values of these distances and a priori information, tomography using traveltime differences provides significantly better resolved results than using traveltimes.     

Evolution of the Upper Rhone River discharge and suspended sediment load during the last 80 years and some implications for Lake Geneva

: During this century, the characteristics of the Upper Rhone River discharge, flowing into Lake Geneva, have been altered in response to the changes which have occurred in its watershed. Principally, numerous hydroelectric dams have been constructed on the course of the Rhone River tributaries. At present the major reservoirs can hold about 122010⁶m³ of water, which represents 1/5 of the total annual Rhone River flow. Flow regime characteristics of the river have been modified by the dam operations. Water is released from reservoirs during winter and stored in summer. Large floods have also been reduced in amplitude and frequency. From the available literature data, sediment rating curves have been calculated and used to estimate the evolution of the sediment load from the Rhone River to Lake Geneva. They show that sediment input has decreased by at least a factor 2. This reduction has impacted the occurrence of underflows along the lake bottom, due to the reduction of sediment-laden floods, which in turn may have considerable negative effects on the reoxygenation of Lake Geneva deep waters.     

The last 750 ka in loess–palaeosol sequences from northern France: environmental background and dating of the western European Palaeolithic

This study presents an overview of Middle Pleistocene loess–palaeosol sequences (LPS) in northern France and discusses the palaeoclimatic significance of the pedosedimentary record in the context of western European LPS and of global climatic cycles for the last 750 ka. In this area, the oldest loess deposits (early Middle Pleistocene) are preserved in sedimentary traps (leeward scarps of fluvial terraces and dissolution sinkholes). They result from local deflation processes reworking Pleistocene sandy fluvial deposits or relicts of Tertiary sands. A large extension of typical calcareous loess over the landscape, the Loess Revolution, is then observed during MIS 6, with heavy mineral assemblages testifying to long-distance transport from the polar desert area of the dried eastern Channel. A correlation scheme is proposed between the global records of northern France in continental environments and both global palaeoclimatic records and other main western European LPS. After 30 years of research, northern France LPS stand as a fundamental archive of the impact of interglacial–glacial climatic cycles as well as millennial events. Finally, these works provide a robust chronoclimatic framework for the study of the western European Late Acheulean and Middle Palaeolithic and for the relative dating of the various fluvial terraces that they fossilise.     

Méthodes de quantification des transferts de matiére par les fluides dans les roches métamorphiques déformées

Résumé

Les transferts de matière par les fluides se marquent dans les roches métamorphiques par des différenciations chimiques et minéralogiques. Une approche quantitative des relations entre transferts de matière et déformation passe par l’étude de ces différenciations dans des structures présentant soit un gradient continu de l’intensité de la déformation, soit des sites structuraux distincts. Dans ces structures, la roche initiale est souvent préservée dans des zones protégées. Des bilans de matière, par comparaison de cette analyse initiale avec les différentes roches déformées sont effectuées. Une référence chimique, minéralogique ou volumique est choisie dans des diagrammes où sont reportés les gains ou les pertes des constituants de la roche pour les différentes valeurs possibles de son changement de volume. Les quantités de matière transférée et les variations de volume sont alors lues directement dans les diagrammes ou calculées par des relations générales. Dans des diagrammes de variation chimique, ces résultats sont reportés pour chaque roche transformée, en fonction d’un paramètre de différenciation : intensité de la déformation, de la transfonnation chimique ou minéralogique, position dans la structure de déformation. Suivant les cas, ces diagrammes donnent l’évolution de la mobilité des éléments au cours de la déformation ou de la différenciation chimique, les gradients de changement de volume ou les variations de masse dans la structure de déformation étudiée. Des exemples d’un bilan minéralogique et volumique entre flancs et charnière d’un pli, d’un bilan chimique dans une zone de cisaillement et de l’écriture d’une réaction métamorphique sont présentés. Les différentes étapes d’une approche quantitative des relations entre transfert de matière et déformation sont récapitulés.     

Standardized uncertainty analysis for hydrometry: a review of relevant approaches and implementation examples

Abstract

The water-centric community has continuously made efforts to identify, assess and implement rigorous uncertainty analyses for routine hydrological measurements. This paper reviews some of the most relevant efforts and subsequently demonstrates that the Guide to the expression of uncertainty in measurement (GUM) is a good candidate for estimation of uncertainty intervals for hydrometry. The demonstration is made by implementing the GUM to typical hydrometric applications and comparing the analysis results with those obtained using the Monte Carlo method. The results show that hydrological measurements would benefit from the adoption of the GUM as the working standard, because of its soundness, the availability of software for practical implementation and potential for extending the GUM to hydrological/hydraulic numerical simulations.

Editor D. Koutsoyiannis

Citation Muste, M., Lee, K. and Bertrand-Krajewski, J.-L., 2012. Standardized uncertainty analysis for hydrometry: a review of relevant approaches and implementation examples. Hydrological Sciences Journal, 57 (4), 643–667.     

Modèle de ruissellement,avancement et infiltration pour l'irrigation à la planche sur un sol recouvrant un sous-sol très perméable

Résumé

Développé sur tableur MS Excel, Calhy est un modèle monodimensionnel d'irrigation à la planche sur calan homogène, pour un sol sur horizon sous-jacent très drainant. De type onde cinétique ou onde diffusante, il adapte le modèle de Green et Ampt et l'équation de Manning-Strickler en tenant compte d'une rétention de surface. Avec cinq paramètres, dont deux mesurés pour décrire l'état d'humectation initial du sol et trois optimisés, le modèle reproduit l'avancement du front ruisselé et le débit de colature observés lors d'irrigations sur prairie dans la plaine semi aride de la Crau (Sud de la France). Les paramètres optimisés sont: la conductivité hydraulique à saturation du sol, constante; le coefficient de Strickler et la rétention de surface, décroissants durant la saison avec l'évolution de la flore et du microrelief. Didactique et convivial, le modèle peut aider à optimiser l'irrigation, dans le but d'obtenir l'infiltration désirée en apportant le moins d'eau possible.

Citation Bader, J.-C., Saos, J.-L. & Charron, F. (2010) Modèle de ruissellement, avancement et infiltration pour l'irrigation à la planche sur un sol recouvrant un sous-sol très perméable. Hydrol. Sci. J. 55(2), 177–191.     

Tidal evolution of close binary asteroid systems

We provide a generalized discussion of tidal evolution to arbitrary order in the expansion of the gravitational potential between two spherical bodies of any mass ratio. To accurately reproduce the tidal evolution of a system at separations less than 5 times the radius of the larger primary component, the tidal potential due to the presence of a smaller secondary component is expanded in terms of Legendre polynomials to arbitrary order rather than truncated at leading order as is typically done in studies of well-separated system like the Earth and Moon. The equations of tidal evolution including tidal torques, the changes in spin rates of the components, and the change in semimajor axis (orbital separation) are then derived for binary asteroid systems with circular and equatorial mutual orbits. Accounting for higher-order terms in the tidal potential serves to speed up the tidal evolution of the system leading to underestimates in the time rates of change of the spin rates, semimajor axis, and mean motion in the mutual orbit if such corrections are ignored. Special attention is given to the effect of close orbits on the calculation of material properties of the components, in terms of the rigidity and tidal dissipation function, based on the tidal evolution of the system. It is found that accurate determinations of the physical parameters of the system, e.g., densities, sizes, and current separation, are typically more important than accounting for higher-order terms in the potential when calculating material properties. In the scope of the long-term tidal evolution of the semimajor axis and the component spin rates, correcting for close orbits is a small effect, but for an instantaneous rate of change in spin rate, semimajor axis, or mean motion, the close-orbit correction can be on the order of tens of percent. This work has possible implications for the determination of the Roche limit and for spin-state alteration during close flybys.