Isotope measurements and ground water flow modeling using MODFLOW for understanding environmental changes caused by a well field in semiarid Brazil

Measurements of the environmental isotopes carbon-14 and oxygen-18 and of the electrical conductivity in ground water, together with MODFLOW-88 (DOS) simulations of pumping tests, were used to achieve a detailed understanding of the functioning of an aquifer in the area of a well field. The methodology was applied in the sedimentary basin of the Cariri region, in the south of Ceará State in Brazil. Localized hydraulic connections between adjacent aquifer units could be detected, and mixing ratios for the contributions from the units involved were determined. Cone of depression simulations for a three-year drought period revealed well interference and a drastic lowering of the piezometric level, thereby explaining the hydrogeologic changes and transformations in vegetation that were observed in the area of the well field. The combined use of the modeling tools and the geochemical field observations is shown to provide more detailed insight into the conceptual model of the groundwater flow system.     

L'érosion chimique et l'érosion mécanique à long terme du substrat granitique (Vendée,France)

We calculate the chemical depletion fraction of the granitic bedrock by analysing the rock-soil enrichment of zirconium. In Vendée (France), chemical weathering rates account for 26% of the denudation rates. Such a chemical depletion fraction characterizes temperate regimes. It is three times lower than that of humid tropical regimes. To cite this article: J.-C. Maurin et al., C. R. Geoscience 337 (2005).     

Plate Motion of India and Interseismic Strain in the Nepal Himalaya from GPS and DORIS Measurements

We analyse geodetically estimated deformation across the Nepal Himalaya in order to determine the geodetic rate of shortening between Southern Tibet and India, previously proposed to range from 12 to 21 mm yr^?1. The dataset includes spirit-levelling data along a road going from the Indian to the Tibetan border across Central Nepal, data from the DORIS station on Everest, which has been analysed since 1993, GPS campaign measurements from surveys carried on between 1995 and 2001, as well as data from continuous GPS stations along a transect at the logitude of Kathmandu operated continuously since 1997. The GPS data were processed in International Terrestrial Reference Frame 2000 (ITRF2000), together with the data from 20 International GNSS Service (IGS) stations and then combined using quasi- observation combination analysis (QOCA). Finally, spatially complementary velocities at stations in Southern Tibet, initially determined in ITRF97, were expressed in ITRF2000. After analysing previous studies by different authors, we determined the pole of rotation of the Indian tectonic plate to be located in ITRF2000 at 51.409±1.560° N and ?10.915±5.556°E, with an angular velocity of 0.483±0.015°. Myr^?1. Internal deformation of India is found to be small, corresponding to less than about 2 mm yr^?1 of baseline change between Southern India and the Himalayan piedmont. Based on an elastic dislocation model of interseismic strain and taking into account the uncertainty on India plate motion, the mean convergence rate across Central and Eastern Nepal is estimated to 19±2.5 mm yr^?1, (at the 67% confidence level). The main himalayan thrust (MHT) fault was found to be locked from the surface to a depth of about 20 km over a width of about 115 km. In these regions, the model parameters are well constrained, thanks to the long and continuous time-series from the permanent GPS as well as DORIS data. Further west, a convergence rate of 13.4±5 mm yr^?1, as well as a fault zone, locked over 150 km, are proposed. The slight discrepancy between the geologically estimated deformation rate of 21±1.5 mm yr^?1 and the 19±2.5 mm yr^?1 geodetic rate in Central and Eastern Nepal, as well as the lower geodetic rate in Western Nepal compared to Eastern Nepal, places bounds on possible temporal variations of the pattern and rate of strain in the period between large earthquakes in this region.     

Geodynamic Technique Applied to the Volcanic Activity Forecast of Lanzarote Island in Spain

In accordance with the Agreement of Sino-Spain Science and Technology Cooperation,the Institute of Seismology,SSB of China and the Institute of Astronomy and Geodesy of Spain have together performed research at the Geodynamics Laboratory of Lanzarote(Canary Islands)with geodynamic instrumentation.Researchers conducted observation and then analyzed the data compiled.Researchers using the advanced geodynamic instruments could monitor the volcanic activity and seismicity in order to forecast the volcanic eruption and earthquakes.The results of this paper are obtained from this scientific and technological cooperation of the two institutes between China and Spain.     

Croissance et reproduction de l'omble-chevalier,Salvelinus alpinus (L.), dans le lac de Neuchâtel (Suisse)

The arctic char (Salvelinus alpinus) which has disappeared from Lake Neuchatel near 1963, has been reintroduced into this lake since 1979. In this study, growth and reproduction of char have been analyzed 4 years after reintroduction. Age determination based on scales were more reliable then those based on otoliths. Growth rate decreased from the cohort born in 1979 to the cohort born in 1982. Nevertheless growth of char in Lake Neuchatel is fast compared to other char populations. About 33% of the males were sexually mature in the second year of life. At this age, no females, and in the third year of life, only 18% of the females were mature. Most fish of both sex were mature at an age of 4 years. A high correlation was found for data taken from other authors between fecundity and length of char. The data from Lake Neuchatel char (this study) fit very well with this general relation.      

Première datation UPb des orthogneiss œillés de la zone axiale de la Montagne noire (Sud du Massif central) : nouveaux témoins du magmatisme ordovicien dans la chaı̂ne Varisque

We present new U–Pb results on felsic Augen orthogneisses from the Axial Zone of the Montagne Noire (French Massif Central). The data indicate Ordovician ages, 456±3 and 450±6 Ma for two samples collected at ‘Pont-de-Larn’ and ‘Gorges d'Héric’, respectively. These ages are interpreted as the igneous emplacement age of the granitic protolith. To cite this article: F. Roger et al., C. R. Geoscience 336 (2004).     

Sur la structure,l'âge et l'origine des « brèches de Bosmendiette » (Pyrénées-Atlantiques)

By us considered as Albo-Aptian in age and generated through halokinetic processes, the Bosmendiette breccias have been recently interpreted as Selandian (Palaeocene) globigerine-bearing sediments deposited in sub-marine canyons within a deep trough crossing the Pyrenees, from the Mediterranean Sea to the Atlantic Ocean. These breccias are really azoic in their lower part and contain a scarce microfauna including radolarians and benthic foraminifera at the top of the formation. They are unconformably covered by the Urgo-Aptian limestones and marls and indicate, under opening marine conditions, Lower Cretaceous collapse movements and northward sliding of the Jurassic slumped cover, related to the growth of the Béloscare–Apoura diapir. To cite this article: J. Canérot et al., C. R. Geoscience 336 (2004).     

Frequency Content Evolution of Snow Avalanche Seismic Signals

Seismic signals generated by avalanches have been recorded by theavalanche team of the Universitat de Barcelona at theVallée de la Sionne experimental site (Switzerland) since 1998. During these years avalanches of varying size and flowwere recorded by two sensors located at different positions.In the present paper we show the general features of the running spectra of the seismicsignals for the different type of recorded avalanches. Using this method we are able not only to detect avalanches with low amplitude signals but also to distinguishbetween avalanches and other seismic sources (i.e., local earthquakes) which have thesame frequency content but a different frequency evolution.