Geophysical characterization of the lithological control on the kinematic pattern in a large clayey landslide (Avignonet,French Alps)

Lithology variation is known to have a major control on landslide kinematics, but this effect may remain unnoticed due to low spatial coverage during investigation. The large clayey Avignonet landslide (French Alps) has been widely studied for more than 35 years. Displacement measurements at 38 geodetic stations over the landslide showed that the slide surface velocity dramatically increases below an elevation of about 700 m and that the more active zones are located at the bottom and the south of the landslide. Most of the geotechnical investigation was carried out in the southern part of the landslide where housing development occurred on lacustrine clay layers. In this study, new electrical prospecting all across the unstable area revealed the unexpected presence of a thick resistive layer covering the more elevated area and overlying the laminated clays, which is interpreted as the lower part of moraine deposits. The downslope lithological boundary of this layer was found at around 700 m asl. This boundary coincides with the observed changes in slide velocity and in surface roughness values computed from a LiDAR DTM acquired in 2006. This thick permeable upper layer constitutes a water reservoir, which is likely to influence the hydromechanical mechanism of the landslide. The study suggests a major control of vertical lithological variations on the landslide kinematics, which is highlighted by the relation between slide velocity and electrical resistivity.     

The Voyager 1/Saturn encounter and the cosmogonic shadow effect

If an electrically conducting medium (e.g. a dusty plasma) rotates around a gravitating central body, which possesses an axisymmetric dipole field, the medium is supported to two-thirds by the centrifugal force and to one-third by electromagnetic forces under the condition that the magnetic field is strong enough to controll the motion. If the electromagnetic forces disappear — e.g. by a de-ionisation of the dusty plasma — the medium will fall down to two-thirds of its original central distance. The result of this process will be a cosmogonic shadow effect which is described in some detail.The Voyager 1/Saturn results demonstrate that the macro-structure of the Saturnian ring system can be explained as a result of this effect working at the formation of the system. The agreement between the theoretical results and the observations is better than a few percent.A similar analysis of the asteroidal belt shows that its macro-structure can also be explained by the cosmogonic shadow effect. The agreement between theory and observations is perhaps even better than in the Saturnian ring system.The observational results demonstrate that during their formation both the Saturnian ring and the asteroidal belt passed a plasma state dominated by electromagnetic effects.     

Submersible observations of Equatorial Atlantic mantle: The St. Paul Fracture Zone region

The St. Paul F.Z. is a large structural domain made up of multiple transform faults interrupted by several Intra-Transform Ridge (ITR) spreading segments. Two regions were studied in details by submersible: (1) The ITR short (<20 km in length) segment near 0° 37N–25° 27W and 1° N–27° 42W and (2) The St. Peter and St. Paul's Rocks (SPPR) massif located at 29° 25W (¡3700 m depth). (1) The short ITR segments consist of a magma starved rift valley with recent volcanic activities at 4700 m depth. A geological profile made along the rift valley wall showed localized volcanics (basalts and dykes) which are believed to overlay and intrude the ultramafics. The geological setting and the high ultramafic/volcanic ratio suggest an extremely low magmatic supply and crustal-mantle uplift during lithospheric stretching and denudation. (2) The St. Peter and St. Paul's Rocks (SPPR) massif consists of a sigmoidal ridge within the active transform zone. The SPPR is divided into two different geological domains called the North and the South Ridges. The North Ridge consists of strongly tectonized fault scarps composed of banded and mylonitized peridotite, sporadic gabbros (3900–2500 m) and metabasalts (2700–1700 m). The South Ridge is less tectonized with undeformed, serpentinized spinel lherzolite (2000–1400 m) and basalts. Extensional motion and denudation accompanied by diapirism affected the South Ridge within a transform domain. Instead, the North Ridge was formed during an important strike-slip and faulting motion resulting in the uplifted portion of the St. Paul F.Z. transverse ridge. There is a regional compositional variation of the volcanics where E-MORBs and alkali basalts are produced on the SPPR massif and are comparable to the adjacent northern segments of the Mid-Atlantic Ridge. On the other hand, N and T- MORBs collected from the eastern part of the St. Paul F.Z. (25° 27W IRT) are similar to the volcanics from the southern segments of the MAR. The peridotites exposed in these provinces (SPPR and ITR) are similar in their REE and trace element distribution. Different degrees (3–15%) of partial melting of a mixed composite mantle consisting of spinel and amphibole bearing lherzolite veined with 5–40% clinopyroxenite gave rise to the observed MORBs and alkali basalts.     

Total oxyradical scavenging capacity and cell membrane stability of haemocytes of the Arctic scallop,Chlamys islandicus,following benzo(a)pyrene exposure

Industrial activities, notably oil and gas industries, are expanding in the Arctic. Most of the biomarkers were developed using temperate organisms living at temperatures above 10 degrees C. Little is known about the biomarker responses of organisms living between -1.88 and 5 degrees C. Therefore, assessment of the toxicity of chemicals to cold-water adapted species is required. In this study, the Arctic scallop, Chlamys islandicus, was selected as a key species for bio-monitoring because of wide distribution in Arctic waters and its commercial value. Test animals, stored in seawater at 2 degrees C, were injected with benzo(a)pyrene (diluted in cod liver oil 5 mg ml(-1)) in the adductor muscle every 24 h for four days giving a final dose of 0, 74 and 90.6 mg kg(-1) wet weight for control, low and high dose, respectively. The biomarkers used were total oxyradical scavenging capacity (TOSC) in the digestive gland and cell membrane stability of haemocytes. TOSC values were significantly reduced (ca. 30%) in exposed groups (P < 0.05), indicating a depletion in oxyradical molecular scavengers. The antioxidant defences appeared to be overwhelmed by the reactive oxygen species as the plasma membranes of haemocytes were destabilised (P < 0.05) probably due to lipid peroxidation. These data indicate that reactive oxygen species (ROS) were produced by Arctic scallops via the metabolisation of benzo(a)pyrene at 2 degrees C.     

Petrogenesis of Variscan high-temperature Group A eclogites from the Moldanubian Zone of the Bohemian Massif,Czechoslovakia

High-temperature (HT), Group A eclogites from three localities in the Moldanubian Zone of the Bohemian Massif are interpreted to have formed in the mantle and to have been transported into the crust by their enclosing garnet peridotites during Variscan orogenesis. Garnet and omphacite are compositionally zoned and contain homogeneous cores and retrograde rims. Cores of minerals yield minimum temperatures and pressures of 850 to 985°C and 16.0 to 22.5 kb, based on Fe–Mg exchange between garnet and clinopyroxene and the jadeite content of clinopyroxene. Sugh high temperatures indicate equilibration in, and derivation from, the upper mantle. Trace element compositions, including the REEs, high MgO contents, and high Mg numbers suggest that the rocks formed by high pressure accumulation of garnet and clinopyroxene and variable amounts of trapped melt. Sm-Nd ages determined on four garnet-clinopyroxene pairs from the three localities are 377±20, 342±9, 336±16, and 323±7 Ma. _Nd and initial ⁸⁷Sr/⁸⁶Sr are negatively correlated, varying from +6.7 to -0.1 and 0.7027 to 0.7057, respectively. Field, compositional, and isotopic data indicate that the eclogites were derived from heterogeneous mantle that included depleted and enriched compositions; this heterogeneity may have resulted from subduction processes that occurred prior to the late Variscan collision of Gondwana and Baltica.     

Failure and size effect for notched and unnotched concrete beams

Modelling failure in geomaterials, concrete or other quasi‐brittle materials and proper accounting for size effect, geometry and boundary effects are still pending issues. Regularised failure models are capable of describing size effect on specimens with a specific geometry, but extrapolations to other geometries are rare, mostly because experimental data presenting size effect for different geometries and for the same material are lacking. Three‐point bending fracture tests of geometrically similar notched and unnotched specimens are presented. The experimental results are compared with numerical simulations performed with an integral‐type non‐local model. Comparisons illustrate the shortcomings of this classical formulation, which fails to describe size effect over the investigated range of geometries and sizes. Finally, experimental results are also compared with the universal size effect law. Copyright © 2013 John Wiley & Sons, Ltd.