International Journal of Agricultural Research, Innovation and Technology (IJARIT)
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Quantification du soulèvement tectonique dans le golfe d’Aqaba, faille du Levant
No full textThe Levant Fault, also known as the Dead Sea Fault, is a left-lateral strike-slip fault of about 1200 km long. It extends from north to south, from the Taurus Mountains and the East Anatolian Fault system, to the northern termination of the extensive Red Sea system. The sinistral activity of the Levant Fault, linked to the north- ward displacement of the Arabian Plate relative to the Sinai sub-plate, is now well constrained with a displacement of ∼ 5mm/yr and nearly 107 km of cumulative dis- placement over 20 My. However, the vertical component of this large fault system is still poorly defined. Based on the study of tectonic activity markers in the Gulf of Aqaba and the Strait of Tiran region, this work consists in constraining the archi- tecture of the fault system in its southern termination. Using new high-resolution multibeam bathymetric data collected during two marine campaigns, we have thus defined a new fault model in the Gulf of Aqaba. The uplift of coral terraces to nearly 100 m above the mean sea level in the Gulf of Aqaba and up to 500 m on the Tiran island, reflects a significant vertical motion over the last few million years. The corals collected on these surfaces during a field trip in March 2017, and analyzed by Uranium-Thorium dating and Strontium isotopy, reveal an establishment of these coral terraces during the interglacial periods. These levels thus serve as temporal markers to constrain the vertical uplift generated by the faults. The precise location of the coral terraces, determined using Pleiades satellite images, allows us to under- stand how the tectonic activity is structured in the Gulf of Aqaba and the Strait of Tiran areas. By correcting the current elevation of the terraces with the eustatic data available in the literature, and by knowing precisely their ages of formation, we deduced the uplift rates of the eastern coast of the Gulf of Aqaba and along the Tiran island. The uplift along the Gulf of Aqaba, estimated using the coral terraces, does not agree with the long-term uplift determined by thermochronology. Further analyses suggest that this uplift is distributed over the off-shore active structures, but also along the on-land structures which were previously considered inactive. This reactivation is due to the change in position of the Arabia-Sinai rotation pole there is 5 My ago. The conclusions of this work raises new questions as to how the de- formation is distributed along this fault section before the change in position of the rotation pole, and how the system is connected to the triple junction Red Sea - Gulf of Suez - Gulf of Aqaba. Is the basin south of the Tiran island is the last pull-apart basin before connecting to the extensive system, or do additional steps, now masked by large evaporite deposits in the Red Sea, propagate further south before connecting to the extensive system?La faille du Levant, également appelée faille de la Mer Morte, est une faille décrochante senestre d’environ 1200 km de long. Elle s’étant du nord au sud, des monts Taurus et du système décrochant de la faille Est Anatolienne, à la terminaison nord du système extensif de la Mer Rouge. L’activité senestre décrochante de la faille du Levant, lié au déplacement vers le nord de la plaque Arabique par rapport à la microplaque Sinaï, est aujourd’hui bien contraint avec un déplacement de ~5mm/an et près de 107 km de décalage cumulé sur 20 Ma. Cependant, la composante verticale de ce grand système de faille reste encore mal définie. A partir de l’étude des marqueurs de l’activité tectonique dans la région du Golfe d’Aqaba et du Détroit de Tiran, les travaux de thèse consistent à contraindre l’architecture du système de faille dans sa terminaison Sud. A l’aide de nouvelles données bathymétrique multifaisceaux hautes résolutions collectées durant deux campagnes marines, nous avons ainsi défini un nouveau modèle de faille dans le golfe d’Aqaba. Le soulèvement de terrasses coralliennes à près de 100 mètres au-dessus du niveau marin dans le golfe d’Aqaba et jusqu’à 500 mètres sur l’île de Tiran, traduis un décalage vertical non négligeable au cours de ces derniers million d’année. Les coraux collectés sur ces surfaces durant la mission de terrain réalisé en Mars 2017, et analysés par datation Uranium-Thorium et isotopie du Strontium, révèlent un établissement de ces terrasses coralliennes pendant les épisodes interglaciaires. Ces niveaux servent ainsi de marqueurs temporels pour contraindre le décalage vertical engendré par les failles. La localisation précise des terrasses coralliennes, déterminée à l’aide d’images satellite Pléiades, permet de comprendre comment se structure l’activité tectonique dans la région du Golfe d’Aqaba et du détroit de Tiran. En corrigeant l’altitude actuelle des terrasses par les données eustatiques disponible dans la littérature et en connaissant précisément leurs âges de formation, nous en avons déduit un taux de soulèvement. Le soulèvement le long du Golfe d’Aqaba, estimé à l’aide des terrasses coralliennes, ne tombe pas en accord avec le soulèvement long terme déterminé par thermochronologie (Lefèvre M., PhD). En poussant l’analyse, il semblerait que ce soulèvement se répartie sur les structures actives mais également le long de structures bordières, jusque lors considérés comme inactives, en raison de la modification de la position du pôle de rotation Arabie-Sinai il y a 5 Ma. L’issue de ces travaux soulève de nouveaux questionnements quant à comment se répartie le décalage le long de cette section de faille avant le changement de position du pôle de rotation, et comment se connecte le système décrochant en direction du point triple Mer Rouge-Golfe de Suez-Golfe d’Aqaba. Le bassin présent au sud de l’île de Tiran est-il le dernier bassin de type pull-apart avant la connexion avec le système extensif, ou est-ce que des échelons supplémentaires, aujourd’hui masqué par les dépôts importants d’évaporite en Mer Rouge, se propage encore plus au Sud avant de se connecter au système extensif
Capabilités et vulnérabilité des Jeunes de 15 à 24 ans à Madagascar
No full textSame of most African countries, the Malagasy population is characterized by its youth, whose average age is 22.4 years. Just over one in five people are between the ages of 15 and 24. Yet the majority of them are poor, do not have access to education and health. It could impact their ability and potential activities. This is the reason why this thesis is interested in the study of the links that may exist between capability and the various variables related to the vulnerability of young people aged 15 to 24 in Madagascar. It should be noted that Sen’s work on capability constitutes the bases of our research. The general methodology of this research was essentially based on the review of the existing scientific literature, the quantitative study based on the use of statistical data available at INSTAT as well as our own qualitative survey on vulnerability and capacities of young people, carried out in the regions of Analamanga and Itasy.Comme beaucoup de pays d’Afrique, la population malgache est caractérisée par sa jeunesse, dont l’âge moyen est de 22,4 ans. Un peu plus d’un individu sur cinq est âgé de 15 à 24 ans. La grande majorité d’entre eux sont pauvres et n’ont pas accès à l’éducation et à la santé, cela pourrait impacter leurs capacités et leurs activités potentielles. C’est la raison pour laquelle cette thèse s’intéresse à l’étude des liens qui peuvent exister entre la capabilité et les différentes variables en rapport à la vulnérabilité des jeunes de 15- 24 ans à Madagascar. Il convient de préciser que les travaux de Sen sur la capabilité constituent la pierre angulaire de notre recherche. La méthodologie générale de cette recherche s’est essentiellement reposée sur la revue de la littérature scientifique existante, sur une étude quantitative basée sur l’exploitation des données statistiques disponibles à l’INSTAT ainsi qu’une enquête qualitative menée par nos soins portant sur la vulnérabilité et les capabilités des jeunes dans les Régions d’Analamanga et d’Itasy
Numerical Simulation of Lunar Seismic Wave Propagation: Investigation of Subsurface Scattering Properties Near Apollo 12 Landing Site
No full textInternational audienceOne of the most critical issues associated with the analysis of lunar seismic data is the intense scattering, which prevents precise seismic phase identifications, thereby resulting in poor constraints on the internal structure of the Moon. Although some studies estimated subsurface scattering properties from analyses of the Apollo seismic data, the properties have large uncertainties and are still open issues to be resolved to improve the inner structure model of the Moon. While the previous studies tried to constrain the scattering features within the lunar crust mainly from data analysis, this study estimated them from a numerical approach. We constrained the scattering properties near Apollo 12 landing site by conducting seismic wave propagation simulations under various parameter settings and comparing the synthetics with the data. As a result, we succeeded in reproducing seismic signals excited by the Apollo artificial impacts. This led to a constraint on the scattering properties, such as typical scale and thickness of heterogeneity, around the Apollo 12 landing site. The derived structure suggests that the intense scattering structure exists down to 20 km at the northern portion of the region of the Apollo 12 landing site, and to 10 km at the southern region from the landing site. In addition, our model requires a smaller P and S wave velocity ratio (1.2-1.4) compared with those conventionally considered (>1.73). This implies a dry and porous environment consistent with laboratory measurements of terrestrial samples and reasonable with the generalized lunar environment
Constraining Jumps in Density and Elastic Properties at the 660 km Discontinuity Using Normal Mode Data via the Backus Gilbert Method
No full textInternational audienceWe apply the Backus Gilbert approach to normal mode center frequency data, to constrain jumps in P, S, bulk sound speed and density at the "660" discontinuity in the earth's mantle (∼650-670 km depth). Different 1 D models are considered to compute sensitivity kernels. When using model PREM (Dziewonski & Anderson, 1981, Physics of the Earth and Planetary Interiors, 25, 297-356. doi:10.1016/0031 9201(81)90046 7) as reference, with a "660" at 670 km depth, the best fitting jumps in density, P and S wave speeds range from (5.1-8.2)%, (5.3-8.0)%, (5.0-7.0)%, respectively, so the PREM values lie outside the ranges of acceptable density and P wave speed jumps. When shifting the depth of "660" to 660 km, the density and S wave speed jumps increase, while the P wave speed jump decreases. Normal mode data do not support a global transition at 650 km depth. The density jumps are closer to those of pyrolite than PREM, while our bulk sound wave speed jumps suggest a larger garnet proportion at "660.
Cerium speciation in silicate glasses: Structure-property relationships
No full textInternational audienceAscertaining elements oxidation state, coordination, and bonding environment provides an understanding of the parameters controlling the elements structural behavior, and in turn, the possibility of developing novel applications. Cerium doped materials are widely used for technological applications, mainly because of the strong UV absorption and the characteristic short decay time of the intense emission in the UV-Vis ranges. In this study, Ce speciation in different glass systems has been evaluated and related to variations in optical and physical properties, as well as to variations in glass network connectivity. Data obtained from X-ray Absorption Spectroscopy, Raman, and Photoluminescence Spectroscopy are presented. By using a multispectroscopy approach, we determined the Ce3+/Ce4+ redox ratio in silicate glasses/melts and the influence of the two different Ce species on structure and properties. Our study indicates that reduced Ce species are favored with an increase in the degree of melt polymerization but hindered in alkaline-rich bulk chemistries. Consequently, the oxygen ion activity (here represented by the theoretical optical basicity) might be used to estimate the Ce redox ratio's evolution. On the contrary, we show that glass luminescence properties cannot be tailored by merely adjusting the bulk chemistry. Furthermore, we propose an alternative approach for detecting and quantifying the different Ce species in glasses, and we show the occurrence of a non-symmetric Raman vibration at ~880 cm-1, whose intensity is well correlated with the Ce3+/Ce4+ redox ratio. We assign this band to the interaction of the SiO4 tetrahedra with Ce4+-O polyhedral. Thus, cerium preferentially links to the silicate network, and we examined the possibility of using Raman spectroscopy to detect and quantify the different Ce species
Lithospheric structure below the currently active Mayotte volcanic area from joint inversion of receiver function and surface wave dispersion data
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Réexamen de la paléogéographie de l'anté-Cénomanien de la zone sud sanaga (Marge Atlantique du Cameroun), à partir de l'analyse de la sismique CameroonSpan et des forages pétroliers.
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