Geogas transport in fractured hard rock – Correlations with mining seismicity at 3.54 km depth, TauTona gold mine, South Africa

An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (The International NELSAM–DAFGAS projects) at the TauTona gold mine, South Africa. Five boreholes up to 60 m long were drilled at 3.54 km depth into the highly fractured Pretorius Fault Zone and instruments for chemical and seismic monitoring installed therein. Over the span of 4 years sensitive gas monitoring devices were continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N₂, 21% O₂, 1% Ar. The geogas components CO₂, CH₄, He and H₂ show the most interesting trends and variations on the minute-by-minute basis and significantly correlate with seismic data, while the ²²²Rn activity remains constant. Time series and cross correlation analysis allow the identification of different gas components (geogas and tunnel air) and the identification of two processes influencing the borehole gas composition: (1) pumping-induced tunnel air breakthrough through networks of initially water-saturated fault fractures; and (2) seismicity induced permeability enhancement of fault fractures to above ∼5 × 10^-10 m². The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ?1 × 10⁹ Nm, located within 1000 m of the cubby) and, it is suggested, also during induced earthquakes, a final goal of the project.     

Colonisation d'une population d'Oscillatoria rubescens (Cyanophyceae) par une bacterie epiphyte

The presence of unknown bacteria upon filaments of the CyanophyteOscillatoria rubescens was observed in the Lake Leman (Lake of Geneva) during Autumn 1985. Conditions of this colonization and the morphology of the association are described. These bacteria probably belong to theCaulobacter group. To explain this colonization we suggest that bacteria respond chemotactically to Cyanophyte exudates.

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Colonisation d'une population d'Oscillatoria rubescens (Cyanophyceae) par une bacterie epiphyte

     

Magnetic mapping of the western Alps: compilation and geological implications

Extracted from large surveys of France, Italy and Switzerland, airborne magnetic data covering the western Alpine Arc have been compiled into a single homogeneous map of magnetic anomalies at the constant altitude of 3000 m. For this purpose, each data set has been revised thoroughly and accurately to give a single coherent large-scale pattern.

The magnetic contour map reflects the anomaly pattern over the entire length of the Western Alpine collision suture. The distribution of polarities exhibits a large anomalous low located by reduction to the pole over the whole external part of the belt. The observed anomaly suggests a large gap of magnetization between the Adriatic microplate and the European crust. The analysis of the waveband shows that the broadest wavelengths are produced in the lower crust close to the transition zone, in the granulite facies. This highly magnetic layer is used as a marker to describe the geometry of the European and Adriatic deep seated crust. The main results are presented on a composite synthetic profile showing the sloping side of the European slab and an important crustal thinning to the southeast of the Adriatic slab. This feature is emphasized on the magnetic contour map by a linear magnetic low attributed to major transcurrent fault. This trend is called the Sestri-Voghera trend and extends from the Ligurian basin by the Sestri-Voltaggio Zone to the Judicarian system. Sinistral movements can be recognized along the whole axis as well as possible uplift of rift shoulders. The magnetic anomaly pattern over the complete length of the anomalous body of Ivrea as well as the Insubric-Canavese Line limit the extension of the Adriatic microplate by a well defined linear trend. The symmetrical shears deduced from consecutive anomalies are used to propose a structural scheme.     

Investigation of coronal mass ejections by the two-position radio sounding method

The two-position radio sounding of the solar wind by the Galileo and Cassini spacecraft has been first performed. These spacecraft followed the Sun from east to west from May 12 to 24, 2000 and sounded the regions spaced in radial directions by several millions of kilometers. Stable correlation has been revealed between fluctuation effects detected in spatially spaced radio-sounding paths of disturbed plasma structures of the coronal mass ejection (CME) type. The radio effects have been found to correlate also with the data on the solar wind density near the Earth orbit. It has been shown that the two-position radio-sounding method together with the data on solar radiation in the X-ray and optic ranges and with the results of local plasma measurements provides information on the structure and velocity of the propagation of CMEs from the photosphere to the Earth orbit. In the most powerful event recorded on May 13, 2000, the CME velocity at the heliocentric distances of about 15R _⊙ (R _⊙ is the solar radius) reached 1200 km/s. At (15–25) R _⊙, the velocity was about 1300 km/s. At distances larger than 25R _⊙, disturbance was decelerated from 1300 to 450 km/s near the Earth orbit.     

Effects of three oil spill dispersants on marine bacterial populations: I. Preliminary Study. Quantitative Evolution of Aerobes

The effects of three hydrocarbon dispersant agents (Corexit 9527, Hydrogamosol LT and OSR LT 126) on the bacterial flora of the marine environment are analysed in 20-square-metre basins filled with lagoon seawater.Four months after the first treatment, oil slicks were no longer visible, whereas the appearance of the untreated reference slick had hardly changed. The treatment of 10-litre crude-oil slicks causes an appreciable and long lasting increase in the bacterial population.     

Intraseasonal atmospheric variability and its interannual modulation in Central Africa

The spatial and temporal structures of the intraseasonal atmospheric variability over central Africa is investigated using 2.5°?×?2.5° daily outgoing longwave radiation (OLR) and National Centers for Environmental Prediction (NCEP) Reanalysis zonal winds for the period 1980–2010. The study begins with an overview of the Central African rainfall regime, noting in particular the contrast amongst Western and Eastern parts, with different topography and surface conditions features. The annual mean rainfall and OLR over the region revealed a zone of intense convective activity centered on the equator near 30°E, which extends southward and covers almost all the Congo forest. The annual cycle of rainfall reflects the classical bi-annual shift of Inter-Tropical Convergence Zone across the equatorial belt, between 10°S and 10°N. The result of the empirical orthogonal functions (EOFs) analysis has shown that the three leading EOF modes explain about 45?% of total intraseasonal variability. The power spectra of all the three corresponding principal components (PCs) peak around 45–50?days, indicating a Madden–Julian Oscillation (MJO) signal. The first mode exhibits high positive loadings over Northern Congo, the second over Southern Ethiopia and the third over Southwestern Tanzania. The PCs time series revealed less interannual modulation of intraseasonal oscillations for the Congo mode, while Ethiopian and Tanzanian modes exhibit strong interannual variations. H?vmoller plots of OLR, 200 and 850?hPa NCEP zonal winds found the eastward propagating features to be the dominant pattern in all the three times series, but this propagation is less pronounced in the OLR than in the 850 and 200?hpa zonal wind anomalies. An index of MJO strength was built by averaging the 30–50?day power for each day. A plot of MJO indices and El Ni?o Southern Oscillation (ENSO) cycle confirm a strong interannual modulation of MJO over Eastern central Africa partially linked with the ENSO events (El Ni?o and La Ni?a). Strong MJO activity is observed during La Ni?a years or during ENSO-neutral years, while weak or absent MJO activity is typically associated with strong El Ni?o episodes.     

Response of Callovo-Oxfordian claystone during drying tests: unsaturated hydromechanical behavior

The French National Agency for Nuclear Waste Management is currently studying the Callovo-Oxfordian claystone as a potential repository for nuclear waste. This study focuses on the hydromechanical (HM) unsaturated response of the rock subjected to hydraulic loading. Static atmosphere drying tests highlighted the HM coupling and mechanical anisotropy of the samples. A coupled poroelastic model was proposed, involving highly nonlinear equations. Numerical simulations were performed using the finite element code Code_Aster. Through a sensitivity analysis, the most suitable parameters for estimation were found to be the Biot coefficient and 3 of the 4 independent parameters of the Van Genuchten?CMualem relations. The parameters were estimated according to an inverse procedure that minimizes a cost functional. The estimates could not outline any hysteretic behavior, but they appeared to be divided into two groups (depending on their fitted values). The convergence and stability of the inverse algorithm were studied, and the results showed that direct computations must be run prior to the inversion to ensure its convergence. No plasticity occurred in the samples (according to the model), whereas irreversible phenomena do take place in situ.     

Liquid water uptake in unconfined Callovo Oxfordian clay-rock studied with neutron and X-ray imaging

The Callovo Oxfordian clay-rock (COx) is studied in France for the disposal of radioactive waste, because of its extremely low permeability. This host rock is governed by a hydromechanical coupling of high complexity. This paper presents an experimental study into the mechanisms of water uptake in small, unconfined, prismatic specimens of COx, motivated by the comprehension of cracking observed during concrete/COx interface sample preparation. Water uptake is monitored using both X-ray tomography and neutron radiography, the combination of these imaging techniques allowing material deformation and water arrival to be quantified, respectively. Given the speed of water entry and crack propagation, relatively fast imaging is required: 5-min X-ray tomographies and 10-s neutron radiographs are used. In this study, pairs of similar COx samples from the same core are tested separately with each imaging technique. Two different orientations with respect to the core are also investigated. Analysis of the resulting images yields with micro- and macro-scale insights into hydromechanical mechanisms to be obtained. This allows the cracking to be interpreted as a rapid breakdown in capillary suction (supposed large both to drying and rebound from in situ stress state) due to water arrival, which in turn causes a loss of effective stress, allowing cracks to propagate and deliver water further into the material.

     

5α(H)-cholestan-3α-ol in sediments: Characterization and geochemical significance

The top five centimeters of sediment collected at the deepest point of Lake Léman (Switzerland), 309 meters below water level, contain concentrations of 5α(H)-cholestan-3α-ol (epicholestanol) up to 10% of the total sterol content. Isobutane chemical ionization mass spectrometry and coinjection with an authentic standard on a SP-1000 glass capillary column were used in order to successfully characterize this epimer of cholestanol.The distribution of this stanol throughout the sediment core studied suggests in situ bacterial production. The change in concentration of epicholestanol with depth is different from those found for other C₂₇ stanols, such as cholestanol or coprostanol. It is probably the result of a change in the bacterial fauna in the most recently deposited sediment, related to the increasing eutrophication of the lake rather than the consequence of its lower stability due to the axial conformation of the OH substituent.