Transferts de matière en zone de subduction. Volume 2 : réflexions sur les conséquences de l'érosion tectonique

Le second et présent volume rappelle tout d'abord les indices à notre disposition d'une érosion tectonique potentielle et examine ensuite les conséquences de l'érosion tectonique. Il s'agit principalement d'un travail bibliographique tendant à répondre aux différentes questions que je me suis posé au cours de ces 5 dernières années. Il servira de rame à mes futures recherches

Frequency shifting of pulsed narrow-band laser light in a multipass Raman cell

A multipass cell is described which allows efficient stimulated Raman frequency shifting for low pump laser intensities and low gas pressures. The latter is important for Raman shifting of narrow-band Fourier-transform limited light pulses (Δv=75 MHz). It is shown that frequency broadening of the Raman shifted light can be largely avoided in the Dicke narrowing regime at low pressures. For 75 MHz pump pulses and an H2 density of 2.5 amagat we found a negligible broadening to 90 MHz of the stimulated Stokes light. This is far below the value of 250 MHz expected from spontaneous emission. The narrow-band Stokes pulses achieved in CO2 enabled us to measure the pressure shift coefficient (-0.71×10-2 cm-1/amagat) of this gas. It is demonstrated, for the example of benzene, that our technique provides a very practical light source for high resolution molecular spectroscopy

Genetic relations between the central and southern Philippine Trench and the Sangihe Trench

International audienceWe surveyed the junction between the central and southern Philippine Trench and the Sangihe Trench near 6øN using swath bathymetry, gravity, and magnetics. These data, along with seismicity, allow us to discuss the genetic relations between these trenches and the forces acting on converging plates. Our final model favors the northern extension of the Halmahera Arc up to 8øN, with three segments offset left-laterally along NW-SE transform faults. Accretion of the northern segment to Mindanao Island 4 to 5 m.y. ago resulted in the failure within the Philippine Sea Plate east of the arc. Initiation of the Philippine Trench between 7øN and 10øN agrees with the maximum recorded depth of the Philippine Trench floor (10,000 m below sea-level) and Philippine Sea slab (200 km). South of 6øN (trench junction), another segment of the arc is being subducted beneath the Sangihe margin, while south of 3øN, the southern segment of the Halmahera Arc is still active. The rapid southward shallowing of the trench floor along the southern Philippine Trench, the type of faulting affecting both sides of the trench, the lack of significant interplate seismicity, and the concentration of the seismicity beneath the Miangas-Talaud Ridge are interpreted as a slowing down of the subduction along this branch of the Philippine Trench compared with the rest of the subduction zone. The Sangihe deformation front has been recognized up to 7øN but seems active only south of 6øN

Towards higher order lattice Boltzmann schemes

In this contribution we extend the Taylor expansion method proposed previously by one of us and establish equivalent partial differential equations of DDH lattice Boltzmann scheme at an arbitrary order of accuracy. We derive formally the associated dynamical equations for classical thermal and linear fluid models in one to three space dimensions. We use this approach to adjust relaxation parameters in order to enforce fourth order accuracy for thermal model and diffusive relaxation modes of the Stokes problem. We apply the resulting scheme for numerical computation of associated eigenmodes and compare our results with analytical references

Reconstructing past terrace fields in the Pyrenees: Insights into land management and settlement from the Bronze Age to the Early Modern era at Vilalta (1650 masl, Cerdagne, France)

© Trustees of Boston University 2015. The building of a solar power station at Thémis, at 1650 masl on the south-facing slope of the Carlit massif in the eastern Pyrenees, led to an archaeological evaluation from April-June 2009. This evaluation covered a surface of 10 ha that included a medieval village as well as the surrounding agricultural land in terraces. Non-destructive archaeological methods were used for the village. A detailed study of the 6 ha of terraces began with a fieldwalking survey, mapping every visible feature, followed by systematic trial trenches. Fifty-five trenches, 11 in the village and 44 in the fields, were opened. The stratigraphies were then compared with a series of 22 radiocarbon dates and eight relative dates provided by ceramic typologies. This combination of surface and buried evidence supported our preliminary hypothesis about the dynamics of the slope. The results suggest the existence of agrarian features beginning in the Bronze Age and reveal that the field patterns were frequently transformed, both in the Medieval and Early Modern periods. The transformations in the terrace fields after the village was abandoned are as interesting as those during occupation because, contrary to the idea of a fixed, unchanging landscape after the end of the Middle Ages, they challenge the idea that mountain zones are marginal spaces by nature, or were marginalized later.Peer Reviewe

Prehistory of Transit Searches

Nowadays the more powerful method to detect extrasolar planets is the transit method. We review the planet transits which were anticipated, searched, and the first ones which were observed all through history. Indeed transits of planets in front of their star were first investigated and studied in the solar system. The first observations of sunspots were sometimes mistaken for transits of unknown planets. The first scientific observation and study of a transit in the solar system was the observation of Mercury transit by Pierre Gassendi in 1631. Because observations of Venus transits could give a way to determine the distance Sun-Earth, transits of Venus were overwhelmingly observed. Some objects which actually do not exist were searched by their hypothetical transits on the Sun, as some examples a Venus satellite and an infra-mercurial planet. We evoke the possibly first use of the hypothesis of an exoplanet transit to explain some periodic variations of the luminosity of a star, namely the star Algol, during the eighteen century. Then we review the predictions of detection of exoplanets by their transits, those predictions being sometimes ancient, and made by astronomers as well as popular science writers. However, these very interesting predictions were never published in peer-reviewed journals specialized in astronomical discoveries and results. A possible transit of the planet beta Pic b was observed in 1981. Shall we see another transit expected for the same planet during 2018? Today, some studies of transits which are connected to hypothetical extraterrestrial civilisations are published in astronomical refereed journals. Some studies which would be classified not long ago as science fiction are now considered as scientific ones.Comment: Submiited to Handbook of Exoplanets (Springer

Seamount Subduction and Megathrust Seismicity: The Interplay Between Geometry and Friction

Subducting seamounts are recognized as one of the key features influencing megathrust earthquakes. However, whether they trigger or arrest ruptures remains debated. Here, we use analog models to study the influence of a single seamount on megathrust earthquakes, separating the effect of topography from that of friction. Four different model configurations have been developed (i.e., flat interface, high and low friction seamount, low friction patch). In our models, the seamount reduces recurrence time, interseismic coupling, and fault strength, suggesting that it acts as a barrier: 80% of the ruptures concentrate in flat regions that surround the seamount and only smaller magnitude earthquakes nucleate above it. The low-friction zone, which mimics the fluid accumulation or the establishment of fracture systems in natural cases, seems to be the most efficient in arresting rupture propagation in our experimental setting