Laboratoire Of Planetologie Et Geodynamique Of Nantes

Nantes, France

Laboratoire Of Planetologie Et Geodynamique Of Nantes

Nantes, France
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Finlay C.C.,Technical University of Denmark | Lesur V.,CNRS Paris Institute of Global Physics | Thebault E.,Laboratoire Of Planetologie Et Geodynamique Of Nantes | Vervelidou F.,German Research Center for Geosciences | And 2 more authors.
Space Science Reviews | Year: 2016

Measurements of the Earth’s magnetic field collected by low-Earth-orbit satellites such as Swarm and CHAMP, as well as at ground observatories, are dominated by sources in the Earth’s interior. However these measurements also contain significant contributions from more rapidly-varying current systems in the ionosphere and magnetosphere. In order to fully exploit magnetic data to probe the physical properties and dynamics of the Earth’s interior, field models with suitable treatments of external sources, and their associated induced signals, are essential. Here we review the methods presently used to construct models of the internal field, focusing on techniques to handle magnetospheric and ionospheric signals. Shortcomings of these techniques often limit the quality, as well as spatial and temporal resolution, of internal field models. We document difficulties in using track-by-track analysis to characterize magnetospheric field fluctuations, differences in internal field models that result from alternative treatments of the quiet-time ionospheric field, and challenges associated with rapidly changing, but spatially correlated, magnetic signatures of polar cap current systems. Possible strategies for improving internal field models are discussed, many of which are described in more detail elsewhere in this volume. © 2016 Springer Science+Business Media Dordrecht

Mangeney A.,CNRS Paris Institute of Global Physics | Roche O.,University Blaise Pascal | Roche O.,Laboratoire Magma et Volcans | Hungr O.,University of British Columbia | And 5 more authors.
Journal of Geophysical Research: Earth Surface | Year: 2010

We describe laboratory experiments of granular material flowing over an inclined plane covered by an erodible bed, designed to mimic erosion processes of natural flows travelling over deposits built up by earlier events. Two controlling parameters are the inclination of the plane and the thickness of the erodible layer. We show that erosion processes can increase the flow mobility (i.e., runout) over slopes with inclination close to the repose angle of the grains θr by up to 40%, even for very thin erodible beds. Erosion efficiency is shown to strongly depend on the slope of the topography. Entrainment begins to affect the flow at inclination angles exceeding a critical angle θc ≃ θr/2. Runout distance increases almost linearly as a function of the thickness of the erodible bed, suggesting that erosion is mainly supply-dependent. Two regimes are observed during granular collapse: a first spreading phase with high velocity followed by a slow thin flow, provided either the slope or the thickness of the erodible bed is high enough. Surprisingly, erosion affects the flow mostly during the deceleration phase and the slow regime. The avalanche excavates the erodible layer immediately at the flow front. Waves are observed behind the front that help to remove grains from the erodible bed. Steep frontal surges are seen at high inclination angles over both rigid or erodible bed. Finally, simple scaling laws are proposed making it possible to obtain a first estimate of the deposit and emplacement time of a granular collapse over a rigid or erodible inclined bed. Copyright 2010 by the American Geophysical Union.

Riaza A.,Geological Survey of Spain | Buzzi J.,Geological Survey of Spain | Garcia-Melendez E.,University of León | Carrere V.,Laboratoire Of Planetologie Et Geodynamique Of Nantes | Muller A.,German Aerospace Center
Remote Sensing | Year: 2011

Monitoring mine waste from sulfide deposits by hyperspectral remote sensing can be used to predict surface water quality by quantitatively estimating acid drainage and metal contamination on a yearly basis. In addition, analysis of the mineralogy of surface crusts rich in soluble salts can provide a record of annual humidity and temperature. In fact, temporal monitoring of salt efflorescence from mine wastes at a mine site in the Iberian Pyrite Belt (Huelva, Spain) has been achieved using hyperspectral airborne Hymap data. Furthermore, climate variability estimates are possible based on oxidation stages derived from well-known sequences of minerals, by tracing sulfide oxidation intensity using archive spectral libraries. Thus, airborne and spaceborne hyperspectral remote sensing data can be used to provide a short-term record of climate change, and represent a useful set of tools for assessing environmental geoindicators in semi-arid areas. Spectral and geomorphological indicators can be monitored on a regular basis through image processing, supported by field and laboratory spectral data. In fact, hyperspectral image analysis is one of the methods selected by the Joint Research Centre of the European Community (Ispra, Italy) to study abandoned mine sites, in order to assess the enforcement of the European Mine Waste Directive (2006/21/EC of the European Parliament and of the Council 15 March 2006) on the management of waste from extractive industries (Official Journal of the European Union, 11 April 2006). The pyrite belt in Andalucia has been selected as one of the core mission test sites for the PECOMINES II program (Cracow, November 2005), using imaging spectroscopy; and this technique is expected to be implemented as a monitoring tool by the Environmental Net of Andalucía (REDIAM, Junta de Andalucía, Spain). © 2011 by the authors.

Neres M.,University of Lisbon | Neres M.,Toulouse 1 University Capitole | Bouchez J.L.,Toulouse 1 University Capitole | Terrinha P.,University of Lisbon | And 7 more authors.
Geophysical Journal International | Year: 2014

The intrusion mechanism and internal structure of sills are still under debate. We present a detailed magnetic study, including anisotropy of magnetic susceptibility and rock magnetic analyses of a Cretaceous (94 Ma), 7-m-thick sill from the Lusitanian Basin in Portugal, the Foz da Fonte sill. The results, from both the top surface and a vertical profile, allow us to propose a model for the magmatic flow pattern and sense of flow. According to their location in the vertical profile, three magnetic fabric domains are identified: (1) at the borders, qualified as chilled margins (~0-50 cm), low anisotropies suggest that low velocity gradients and heterogeneous flow paths occurred during the initial emplacement stages; (2) in the centre of the sill, where low anisotropies are observed, low shear gradients and magma displacement close to pure translation is inferred and (3) in the intermediate zones, high anisotropy values are ascribed to zones having undergone high shear gradients. The mean magnetic lineations from the top surface and basal contact indicate an almost horizontal and NW-SE orientation (azimuth: 310°) which agrees with the preferred orientation of iron oxide grain clusters and with the elongation of vesicles considered as coaxial with the magma flow direction. Moreover, the magnetic foliation planes and the lineations show both a mirror imbrication relative to the average upper and lower border surfaces of the sill, pointing to a flow direction towards the SE. Based on these results and on the interpretation of two seismic reflection lines, we show that the Cabo Raso magnetic anomaly, located 25 km to NW of the FF-sill, is associated to Cretaceous magmatic intrusions from which the sill likely originated. This tectono-magmatic setting is discussed with respect to the West Iberia Late Cretaceous magmatism, integrating magnetic anomalies, isotope chronology and tectonics. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Riaza A.,Geological Survey of Spain | Buzzi J.,Geological Survey of Spain | Garcia-Melendez E.,University of León | Vazquez I.,Geological Survey of Spain | And 3 more authors.
Environmental Earth Sciences | Year: 2012

Hyperspectral low spatial resolution Hyperion data are used to map mine waste from massive sulphide ore deposits, mostly abandoned, on the Iberian Pyrite Belt. Hymap high spatial resolution data are used for crossed interpretation. Mine dams, mill tailings and mine dumps in a variable state of pyrite oxidation are recognizable. Ponds of acid water in the mine sites are spectrally outstanding and, with simple image processing procedures, mappable. In addition, acid water with different chemical composition is mappable with hyperspectral data, whether of high or low spatial resolution. A sequence of hyperspectral image processing algorithms used to produce the maps is suggested. Therefore, hyperspectral data are invaluable in giving quick hints on the quality of the rapidly changing state of the contamination generated by sulphide mine waste, enabling the authorities to activate mitigation procedures. © 2011 Springer-Verlag.

Moretti L.,CNRS Paris Institute of Global Physics | Moretti L.,University Paris Diderot | Mangeney A.,CNRS Paris Institute of Global Physics | Mangeney A.,University Paris Diderot | And 6 more authors.
Geophysical Research Letters | Year: 2012

The rock-ice avalanche that occurred in 2005 on Mount Steller, Alaska and the resulting long period seismic waves have been simulated for different avalanche scenarios (i.e., flow histories), with and without erosion processes taken into account. This 40-60 Mm 3 avalanche traveled about 10 km down the slope, mainly on top of a glacier, eroding a significant amount of ice. It was recorded by 7 broadband seismic stations. The simulations were compared with the recorded long period seismic signal and with the inverted flow history. The results show that, when erosion processes are taken into account, the simulations reproduce the observed signal at all the stations over a wide range of azimuths and source-station distances (37-623 km). This comparison makes it possible to constrain the rheological parameters involved which should help constrain the volume of eroded material. Because landslides are continuously recorded by seismic networks, this method could significantly broaden quantitative insights into natural flow dynamics. © 2012. American Geophysical Union. All Rights Reserved.

Moretti L.,CNRS Paris Institute of Global Physics | Allstadt K.,University of Washington | Mangeney A.,CNRS Paris Institute of Global Physics | Mangeney A.,French Institute for Research in Computer Science and Automation | And 4 more authors.
Journal of Geophysical Research B: Solid Earth | Year: 2015

We focus on the 6 August 2010 Mount Meager landslide that occurred in Southwest British Columbia, Canada. This 48.5Mm3 rockslide that rapidly changed into a debris flow was recorded by over 25 broadband seismic stations. We showed that the waveform inversion of the seismic signal making it possible to calculate the time history of the force applied by the landslide to the ground is very robust and stable, even when using only data from a single station. By comparing this force with the force calculated through numerical modeling of the landslide, we are able to support the interpretation of seismic data made using a simple block model. However, our study gives different values of the friction coefficients involved and more details about the volumes and orientation of the subevents and the flow trajectory and velocity. Our sensitivity analysis shows that the characteristics of the released mass and the friction coefficients all contribute to the amplitude and the phase of the force. Despite this complexity, our study makes it possible to discriminate the best values of all these parameters. Our results suggest that comparing simulated and inverted forces helps to identify appropriate rheological laws for natural flows. We also show that except for the initial collapse, peaks in the low-frequency force related to bends and runup over topography changes are associated with high-frequency generation, possibly due to an increased agitation of the granular material involved. ©2015. American Geophysical Union. All Rights Reserved.

Vasavada A.R.,Jet Propulsion Laboratory | Grotzinger J.P.,California Institute of Technology | Arvidson R.E.,Washington University in St. Louis | Calef F.J.,Jet Propulsion Laboratory | And 9 more authors.
Journal of Geophysical Research E: Planets | Year: 2014

The Mars Science Laboratory mission reached Bradbury Landing in August 2012. In its first 500 sols, the rover Curiosity was commissioned and began its investigation of the habitability of past and present environments within Gale Crater. Curiosity traversed eastward toward Glenelg, investigating a boulder with a highly alkaline basaltic composition, encountering numerous exposures of outcropping pebble conglomerate, and sampling aeolian sediment at Rocknest and lacustrine mudstones at Yellowknife Bay. On sol 324, the mission turned its focus southwest, beginning a year-long journey to the lower reaches of Mt. Sharp, with brief stops at the Darwin and Cooperstown waypoints. The unprecedented complexity of the rover and payload systems posed challenges to science operations, as did a number of anomalies. Operational processes were revised to include additional opportunities for advance planning by the science and engineering teams. Key Points Curiosity has investigated the habitability of Gale Crater, Mars Curiosity has explored environments with evidence of ancient fluvial activity The unprecedented complexity of the rover challenged science operations ©2014. American Geophysical Union. All Rights Reserved.

Zhao J.,University Paris Diderot | Zhao J.,Wuhan University | Moretti L.,University Paris Diderot | Mangeney A.,University Paris Diderot | And 12 more authors.
Pure and Applied Geophysics | Year: 2015

The seismic signals generated by two large volcanic debris avalanches (Montserrat, Lesser Antilles, 1997 and Mount St. Helens, USA, 1980) and a large rock-ice avalanche (Mount Steller, USA, 2005) have been analyzed. For the two debris avalanches, given the times and locations of such landslides, their signals were recorded by only a few seismic stations. Moreover, these signals cover only a very narrow frequency band and include considerable noise. The Mount Steller, on the contrary, was precisely recorded. For each event, the source mechanism (i.e., point force) has been determined by waveform inversion using at most two broadband seismic stations. The resulting force is very difficult to interpret in terms of landslide characteristics. A Monte-Carlo inversion was therefore performed by imposing a simple force model associated with the landslide, based on the schematic view of an accelerating/decelerating mass traveling down the slope. The best parameter set of the force model was then found by minimizing misfits and maximizing correlations between data and synthetic signals. This model appears to contain the minimum degree of complexity required to well reproduce the seismic data. We detail here the method for the Montserrat debris avalanche and then present it’s validation on the well studied Mount St. Helens debris avalanche and the well recorded Mount Steller rock-ice avalanche. The horizontal and vertical components of the resulting force have different source time functions. The best force model compares well with the force obtained by waveform inversion. Finally, this simple force model was interpreted using analytical and empirical relations derived from the sliding block model, granular flow model and landslide studies. This made it possible to estimate the order of magnitude of the mass, flow duration and direction, initial topography slope, mean velocity and travel distance of the avalanches. For these three avalanches, the calculated characteristics are consistent with former studies. © 2014 Springer Basel.

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