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71.
Jérôme GATTACCECA Millarca VALENZUELA Minoru UEHARA A. J. Timothy JULL Marlène GISCARD Pierre ROCHETTE Régis BRAUCHER Clement SUAVET Matthieu GOUNELLE Diego MORATA Pablo MUNAYCO Michèle BOUROT‐DENISE Didier BOURLES François DEMORY 《Meteoritics & planetary science》2011,46(9):1276-1287
Abstract– We describe the geological, morphological, and climatic setting of the San Juan meteorite collection area in the Central Depression of the Atacama Desert (Chile). Our recovery activities yielded 48 meteorites corresponding to a minimum of 36 different falls within a 3.88 km2 area. The recovery density is in the range 9–12 falls km?2 depending on pairing, making it the densest among meteorite collection areas in hot deserts. This high meteorite concentration is linked to the long‐standing hyperaridity of the area, the stability of the surface pebbles (> Ma), and very low erosion rates of surface pebbles (approximately 30 cm Ma?1 maximum). The San Juan meteorite population is characterized by old terrestrial ages that range from zero to beyond 40 ka, and limited weathering compared with other dense collection areas in hot desert. Chemical weathering in San Juan is slow and mainly controlled by the initial porosity of meteorites. As in the Antarctic and other hot deserts, there is an overabundance of H chondrites and a shortage of LL chondrites compared with the modern falls population, suggesting a recent (< few ka) change in the composition of the meteorite flux to Earth. 相似文献
72.
As in the observed record, the termination of El Niño in the coupled IPCC-AR4 climate models involves meridional processes tied to the seasonal cycle. These meridional processes both precondition the termination of El Niño events in general and lead to a peculiar termination of extreme El Niño events (such as those of 1982–83 and 1997–98), in which the eastern equatorial Pacific warm sea surface temperature anomalies (SSTA) persist well into boreal spring/early-summer. The mechanisms controlling the peculiar termination of extreme El Niño events, which involves to the development of an equatorially centred intertropical convergence zone, are consistent across the four models that exhibit extreme El Niños and observational record, suggesting that this peculiar termination represents a general feature of extreme El Niños. Further, due to their unusual termination, extreme El Niños exhibit an apparent eastward propagation of their SSTA, which can strongly influence estimates of the apparent propagation of ENSO over multi-decadal periods. Interpreting these propagation changes as evidence of changes in the underlying dynamical feedbacks behind El Niño could therefore be misleading, given the strong influence of a single extreme event. 相似文献
73.
The Mt Cameroon volcano is the highest and most active volcano of the Cameroon Volcanic Line. Little geological information
is available for improving the understanding of the structure of this large volcanic system and its relationship to regional
tectonics. After reviewing the tectonic evolution of the region, the analysis of a Digital Elevation Model and results from
a field campaign dedicated to mapping geological structures in the summit area and at the SE base of Mt Cameroon are presented.
Mt Cameroon is a lava-dominated volcano with long steep (over 30°) flanks. It is elongate parallel to its well defined rift
zone. The summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults. Geological profiles
were measured along rivers cutting through a topographic step at the SE base of Mt Cameroon. This step is associated with
deformed Miocene sediments from the Douala basin that are overlain by volcanic products. Weak sediments of this area are deformed
by 050°–060° and 020°–030° trending asymmetrical folds verging toward the SE, and thrusts faults related to the spreading
of the volcano over its mechanically weak substratum. Combined remote sensing and field observations suggest that spreading
is accommodated by summit subsidence and flanks sliding. Both slow spreading movements and catastrophic collapses of the steep
flanks are interpreted to result from complex interactions between the growing edifice, repeated dyke intrusions, the weak
sedimentary substratum and tectonic structures. 相似文献
74.
The development of coastal ocean modeling in the recent years has allowed an improved representation of the associated complex
physics. Such models have become more realistic, to the point that they can now be used to design observation networks in
coastal areas, with the idea that a “good” network is a network that controls model state error. To test this ability without
performing data assimilation, we set up a technique called Representer Matrix Spectra (RMS) technique that combines the model
state and observation error covariance matrices into a single scaled representer matrix. Examination of the spectrum and the
eigenvectors of that matrix informs us on which model state error modes a network can detect and constrain amidst the observation
error background. We applied our technique to a 3D coastal model in the Bay of Biscay, with a focus on mesoscale activity,
and tested the performance of various altimetry networks and an in situ array deployment strategy. It appears that a single
nadir altimeter is not efficient enough at capturing coastal mesoscale physics, while a wide swath altimeter would do a much
better job. Testing various local in situ array configurations confirms that adding a current meter to a vertical temperature
measurement array improves the detection of secondary variability modes, while shifting the array higher on the shelf break
would obviously enhance the model constraint along the coast. The RMS technique is easily set up and used as a “black box,”
but the utility of its results is maximized by previous knowledge of model state error physics. The technique provides both
quantitative (eigenvalues) and qualitative (eigenvectors) tools to study and compare various network options. The qualitative
approach is essential to discard possibly inconsistent modes. 相似文献
75.
76.
Marie Lefrancq Paul Van Dijk Victor Jetten Matthieu Schwob Sylvain Payraudeau 《水文研究》2017,31(6):1408-1423
Predicting runoff hot spots and hot‐moments within a headwater crop‐catchment is of the utmost importance to reduce adverse effects on aquatic ecosystems by adapting land use management to control runoff. Reliable predictions of runoff patterns during a crop growing season remain challenging. This is mainly due to the large spatial and temporal variations of topsoil hydraulic properties controlled by complex interactions between weather, growing vegetation, and cropping operations. This interaction can significantly modify runoff patterns and few process‐based models can integrate this evolution of topsoil properties during a crop growing season at the catchment scale. Therefore, the purpose of this study was to better constrain the event‐based hydrological model Limburg Soil Erosion Model by incorporating temporal constraints for input topsoil properties during a crop growing season (LISEM). The results of the temporal constraint strategy (TCS) were compared with a classical event per event calibration strategy (EES) using multi‐scale runoff information (from plot to catchment). The EES and TCS approaches were applied in a loess catchment of 47 ha located 30 km northeast of Strasbourg (Alsace, France). A slight decrease of the Nash–Sutcliffe efficiency criterion on runoff discharge for TCS compared to EES was counterbalanced by a clear improvement of the spatial runoff patterns within the catchment. This study showed that limited agronomical and climatic information added during the calibration step improved the spatial runoff predictions of an event‐based model. Reliable prediction of runoff source, connectivity, and dynamics can then be derived and discussed with stakeholders to identify runoff hot spots and hot‐moments for subsequent land use and crop management modifications. 相似文献
77.
Matthieu Dumont Said Taibi Jean-Marie Fleureau Nabil Abou Bekr Abdelghani Saouab 《Comptes Rendus Geoscience》2010,342(12):892-900
A simple thermohydromechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. 相似文献
78.
Matthieu Kervyn Gerald G. J. Ernst Jurgis Klaudius Jörg Keller François Kervyn Hannes B. Mattsson Frederic Belton Evelyne Mbede Patric Jacobs 《Bulletin of Volcanology》2008,70(9):1069-1086
The largest natrocarbonatite lava flow eruption ever documented at Oldoinyo Lengai, NW Tanzania, occurred from March 25 to
April 5, 2006, in two main phases. It was associated with hornito collapse, rapid extrusion of lava covering a third of the
crater and emplacement of a 3-km long compound rubbly pahoehoe to blocky aa-like flow on the W flank. The eruption was followed
by rapid enlargement of a pit crater. The erupted natrocarbonatite lava has high silica content (3% SiO2). The eruption chronology is reconstructed from eyewitness and news media reports and Moderate Resolution Imaging Spectroradiometer
(MODIS) satellite data, which provide the most reliable evidence to constrain the eruption’s onset and variations in activity.
The eruption products were mapped in the field and the total erupted lava volume estimated at 9.2 ± 3.0 × 105 m3. The event chronology and field evidence are consistent with vent construct instability causing magma mixing and rapid extrusion
from shallow reservoirs. It provides new insights into and highlights the evolution of the shallow magmatic system at this
unique natrocarbonatite volcano. 相似文献
79.
Jean-Paul Toutain Margot Munoz Jean-Louis Pinaud Stéphanie Levet Matthieu Sylvander Alexis Rigo Jocelyne Escalier 《Pure and Applied Geophysics》2006,163(4):723-744
Groundwater coseismic transient anomalies are evidenced and characterized by modelling the mixing function F characteristic
of the groundwater dynamics in the Ogeu (western French Pyrénées) seismic context. Investigations of water-rock interactions
at Ogeu indicate that these mineral waters from sedimentary environments result from the mixing of deep waters with evaporitic
signature with surficial karstic waters. A 3-year hydrochemical monitoring of Ogeu springwater evidences that using arbitrary
thresholds constituted by the mean ± 1 or 2σ, as often performed in such studies, is not a suitable approach to characterize transient anomalies. Instead, we have used
a mixing function F calculated with chemical elements, which display a conservative behavior not controlled by the precipitation of a mineral
phase. F is processed with seismic energy release (Es) and effective rainfalls (R). Linear impulse responses of F to Es and R have been calculated. Rapid responses (10 days) to rainwater inputs are evidenced, consisting in the recharge of the shallow
karstic reservoir by fresh water. Complex impulse response of F to microseismic activity is also evidenced. It consists in a 2-phase hydrologic signal, with an inflow of saline water in
the shallow reservoir with a response delay of 10 days, followed by an inflow of karstic water with a response delay of 70
days, the amount being higher than the saline inflow. Such a process probably results from changes in volumetric strain with
subsequent microfracturation transient episodes allowing short inflow of deep salted water in the aquifer. This study demonstrates
that groundwater systems in such environments are unstable systems that are highly sensitive to both rainfall inputs and microseismic
activity. Impulse responses calculation of F to Es is shown to be a powerful tool to identify transient anomalies. Similar processing is suggested to be potentially efficient
to detect precursors of earthquakes when long time-series (5 years at least) are available in areas with high seismicity. 相似文献
80.
Pierre ROCHETTE Jérôme GATTACCECA Lydie BONAL Michèle BOUROT‐DENISE Vincent CHEVRIER Jean‐Pierre CLERC Guy CONSOLMAGNO Luigi FOLCO Matthieu GOUNELLE Tomas KOHOUT Lauri PESONEN Eric QUIRICO Leonardo SAGNOTTI Anna SKRIPNIK 《Meteoritics & planetary science》2008,43(5):959-980
Abstract— A database of magnetic susceptibility (χ) measurements on different non‐ordinary chondrites (C, E, R, and ungrouped) populations is presented and compared to our previous similar work on ordinary chondrites. It provides an exhaustive study of the amount of iron‐nickel magnetic phases (essentially metal and magnetite) in these meteorites. In contrast with all the other classes, CM and CV show a wide range of magnetic mineral content, with a two orders of magnitude variation of χ. Whether this is due to primary parent body differences, metamorphism or alteration, remains unclear. C3–4 and C2 yield similar χ values to the ones shown by CK and CM, respectively. By order of increasing χ, the classes with well‐grouped χ are: R << CO < CK ≈ CI < Kak < CR < E ≈ CH < CB. Based on magnetism, EH and EL classes have indistinguishable metal content. Outliers that we suggest may need to have their classifications reconsidered are Acfer 202 (CO), Elephant Moraine (EET) 96026 (C4–5), Meteorite Hills (MET) 01149, and Northwest Africa (NWA) 521 (CK), Asuka (A)‐88198, LaPaz Icefield (LAP) 031156, and Sahara 98248 (R). χ values can also be used to define affinities of ungrouped chondrites, and propose pairing, particularly in the case of CM and CV meteorites. 相似文献