Sismotectonique et socle tardi-hercynien réactivé au Sud-Est de la France .

13 pagesIn the Provencal basement, a prefaulted late Hercynian system, hidden beneath the Meso-Cenozoic cover, is evidenced from seismic distribution and analysis of focal mechanisms. This system extends roughly in a N40° to N50° direction from the Durance fault betwen the Argentera and Pelvoux Massifs. It is composed of senestrial strike-slip faults with a small inverse component which is more important in the South-western part of the zone in front of the Digne nappe. The lateral extrusion of a block which is delimited to the North with the Belledonne-Mont Blanc dextral fault and to the South with our senestrial strike-slip faults system is consistent with the dextral strike-slip system which follows the bend of the external western border of the Alpine belt. It also agrees with the geodynamical model at present admitted for the Alps namely a post-collision regime limited to the end of the convergence of Apulian and African plates with a likely conterclockwise rotation of the Adriatic plate. Finaly the lateral extrusion of the block may be responsible for the ondulation of the basement and the derived overlaps of the Lure Moutain

Searching for chaotic deterministic features in laboratory water surface waves

International audienceThe dynamic evolution of laboratory water surface waves has been studied within the framework of dynamical systems with the aim to identify stochastic or deterministic nonlinear features. Three different regimes are considered: pure wind waves, pure mechanical waves and mixed (wind and mechanical) waves. These three regimes show different dynamics. The results on wind waves do not clearly support the recently proposed idea that a deterministic Stokes-like component dominate the evolution of such waves; they are more appropriately described by a similarity-like approach that includes a random character. Cubic resonant interactions are clearly identified in pure mechanical waves using tricoherence functions. However, detailed aspects of the interactions do not fully agree with existing theoretical models. Finally, a deterministic motion is observed in mixed waves, which therefore are best described by a low dimensional nonlinear deterministic process

Coagulation of bentonite suspension by polyelectrolytes or ferric chloride: floc breakage and reformation

International audienceCoagulation process usually involves different hydrodynamic conditions, in particular when it is followed by a filtration step. In this study, coagulation performance was investigated under a wide range of shear stress. Floc behaviour was followed in-line by laser granulometry to determine size distribution and structure. Synthetic suspension of bentonite in tap water was used as a reference for mineral solids in surface water. Three cationic polymers (polyamine based and polyDADMAC) and ferric chloride were tested using different coagulation reactor geometries. Jar-test indicated coagulation performance under mild hydrodynamic conditions and Taylor-Couette reactors were used to create shear stresses up to 8 Pa. Flocs formed with ferric chloride are not able to grow under middle shear stress like 1.5 Pa. On the contrary, polyelectrolytes lead to large flocs, dense (Df = 2.6) and resistant to shear stress. A qualitative comparison of floc resistance to shear depending on hydrodynamic conditions and coagulant type is given through the calculation of the strength factor. Fractal dimension measurements indicate a mechanism of particle erosion when flocs are subjected to a higher shear stress in Taylor-Couette reactor. Floc re-growth is also investigated, and breakage appears to be non-reversible regardless of coagulant and conditions experimented

Shoreline change of the Mekong River delta along the southern part of the South China Sea coast using satellite image analysis (1973-2014)

16th Young Geomorphologists Days, Nantes, FRANCE, JAN 29-30, 2015International audienceThe Mekong River delta is the world's third largest delta, consequence of a favourable morphosedimentary setting, high sediment supply and rapid growth during the Holocene. Analysis of Landsat satellite images from 1973 to 2014 shows that nearly 70% of the 160km - long South China Sea shoreline of the delta has strongly eroded. This trend represents a reversal of the massive, long-term Holocene progradation that characterized this part of the delta. Erosion and land loss along the South China Sea coast are not related to lobe switching, but more likely to decreasing river sediment supply and variations in patterns of sediment storage in the delta that appear to be due to human-induced modifications. These include fluvial sediment trapping by dams, enhanced subsidence due to massive groundwater abstraction, and riverbed aggregate extractions. Shoreline erosion is further exacerbated by the replacement of protective mangroves by shrimp farms. This erosion constitutes an additional hazard to the future integrity of a mega-delta already considered particularly vulnerable to subsidence, and to future large-capacity dams

Estimation du charriage par acoustique passive.

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The impact of Cyclone Nargis on the Ayeyarwady (Irrawaddy) River delta shoreline and nearshore zone (Myanmar): Towards degraded delta resilience?

International audienceThe Ayeyarwady River delta (Myanmar) is exposed to tropical cyclones, of which the most devastating has been cyclone Nargis (2-4 May 2008). We analysed waves, flooded area, nearshore suspended sediments, and shoreline change from satellite images. Suspended sediment concentrations up to 40% above average during the cyclone may reflect fluvial mud supply following heavy rainfall and wave reworking of shoreface mud. Massive recession of the high-water line resulted from backshore flooding by cyclone surge. The shoreline showed a mean retreat of 47 m following Nargis. Erosion was stronger afterwards (-148 m between August 2008 and April 2010), largely exceeding rates prior to Nargis (2000-2005: -2.14 m/year) and over 41 years (1974-2015: -0.62 m/year). This implies that resilience was weak following cyclone impact. Consequently, the increasingly more populous Ayeyarwady delta, rendered more and more vulnerable by decreasing fluvial sediment supply, could, potentially, become more severely impacted by future high-energy events

Modern pollen-based biome reconstructions in East Africa expanded to southern Tanzania

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