Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The active collision zone around Taiwan orogen receives a variety of sedimentary inputs, including terrigenous flux from Taiwan and Chinese rivers, oceanic currents and atmospheric dust. In order to determine the present-day respective contributions of these different sources, we analysed the Pb and Sr isotopic compositions of late Quaternary sediments accumulated offshore east Taiwan. Samples from the Taiwan Coastal Range (andesites, sandstones, conglomerate and Peinan River terraces and suspended loads) have also been analysed to constrain the mean Taiwan isotopic signature. Mixing lines between the different sources of material indicate that the core located in the Okinawa Trough represents a mixture of about 60% of Taiwan, 30% of Chinese Loess and 10% of Yangtze River contributions. The southernmost core, located close to Luzon Are, is influenced by Taiwan (60%) and volcanic material (40%). The Sr and Pb isotopic compositions of samples cored in the Manila Trench and in the Huatung Basin are strongly influenced by the Taiwan signature, while the Ryukyu Trench core samples point to significant but variable contributions of Chinese Loess and Yangtze River. This work also reports Zn isotopic variations in the silicate fraction of these marine core samples. The overall variation in Zn isotopic compositions (expressed as 666 Zn) is greater than 0.3 per mil (parts per thousand) for an analytical precision of +/- 0.05 parts per thousand. The Zn isotopic signal for most of the marine core samples is similar to the literature data measured on sedimentary material, except for the Manila Trench core samples and the older sample from the Huatung Basin: they present values heavier by 0.2-0.3 parts per thousand, close to those obtained on all Taiwan rocks and Peinan River particulates. These results show: 1- the particular characteristics of Taiwan Zn isotopic compositions on a large scale; and: 2- the possible use of Zn isotopes as a tracer of material sources.
ISSN: 0009-2541

hal-00412214
https://hal.archives-ouvertes.fr/hal-00412214
DOI : 10.1016/j.chemgeo.2007.10.024

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : Yellowfin tuna (Thunnus albacares) is a main target for the fisheries at Fish Aggregating Devices (FADs) off the south of Okinawa island. Catch and weight composition of the tuna were monitored at a fisheries cooperative market from 1989 to 1998. Some distinct weight groups (considered to represent cohorts) appeared in the catch and the weight of these groups increased monthly - presumably as individual tuna grew. Although small, light weight fish were caught year-round, the 2 kg weight group that was recruited in May grew to about 15 kg by May of the next year. There was a significant seasonal cycle in the monthly catches. The catch of heavier weight groups decreased in winter indicating the tuna moved out of this FAD area. At one of huge FADs (Nirai), fifteen nautical miles southeast of Okinawa island (depth about 1.300 m), a current meter (Aanderaa RCM-7) recorded current and water temperature from June 1995 to March 1996. The current meter was attached to the FAD at 4 m depth. When typhoons attacked Okinawa, the water temperature drastically dropped. Typically, average current speed was 29 cm/s and eastward current was most frequent. Being affected by tide, the current was averaged over twenty-five hours. Current speed was correlated with the yellowfin catch in 120 daily sets at the FAD; the weaker the current speed, the greater the catch. Although not significant, the catch was greater with northeastward current than with southwestward current.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15300/12662.pdf
http://archimer.ifremer.fr/doc/00042/15300/

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 × 200 km2 area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15–18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a mid-lithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho but with a more slanting direction (NE–SW) compared to the NS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8–9 per cent. We relate this interface to melt ponding, possibly favouring here deformation process such as grain-boundary sliding (EAGBS) due to lithospheric strain. Its geometry might have been controlled by inherited lithospheric fabrics and heterogeneous upper mantle structure. We evidence that crustal and mantle magmatic processes represent first order mechanisms to ease and locate the deformation during the first stage of a cratonic lithospheric breakup.
ISSN: 0956-540X

hal-01622078
https://hal.archives-ouvertes.fr/hal-01622078
https://hal.archives-ouvertes.fr/hal-01622078/document
https://hal.archives-ouvertes.fr/hal-01622078/file/plasmanGJI2017.pdf
DOI : 10.1093/gji/ggx177

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : Comme dans d’autres régions du monde, la croissance démographique et l’aménagement côtier sur le littoral acadien au Nouveau-Brunswick contribuent à une plus grande vulnérabilité et à la détérioration des espaces côtiers et environnements littoraux. L’élévation du niveau marin et les effets des changements climatiques rendent les côtes du Nouveau-Brunswick extrêmement sensibles et entrainent des impacts de plus en plus importants. Ainsi, l’adaptation aux changements climatiques constitue un enjeu de taille pour la province.Nous décrivons ici les résultats d’une étude comparative sur les expériences et les stratégies d’adaptation de deux communautés côtières, les communautés de Cocagne - Grande Digue et de Beaubassin-Est - Cap Pelé. Les deux territoires ont en commun d’avoir des littoraux convoités par le tourisme et le secteur immobilier. Des entretiens semi-dirigés et des groupes de discussion (focus groups) ont permis d’obtenir des informations sur les thématiques suivantes : l’expérience des modifications environnementales, les mesures d’adaptation initiées individuellement ou collectivement, les réactions et les besoins futurs. Les résultats de l’étude mettent en évidence l’enchâssement des aspects économiques et sociétaux dans les enjeux environnementaux et le rôle des représentations et des acteurs qui déterminent le niveau de mobilisation. Enfin, le projet souligne l’importance d’une coordination entre les différentes échelles de gouvernance.
As in other parts of the world, population growth and coastal planning on New Brunswick’s Acadian coastline are contributing to greater vulnerability and deterioration of the natural environment. The rise in sea level and the effects of climate change make the coasts of New Brunswick extremely sensitive, leading to impacts that are increasingly larger. Thus, adaptation to climate change is a major challenge for the province.Here, we describe the results of a comparative study of the experiences and coping strategies of two coastal communities: Cocagne – Grande-Digue and Beaubassin East – Cap-Pelé. Both these territories attract tourism and real estate investors. Semi-structured interviews and focus groups were used to obtain information on the following topics: the experience of environmental change, adaptation measures initiated individually or collectively, reactions and future needs. Results of the study highlight the entrenchment of economic and societal aspects of environmental issues and the role of representations and stakeholders that determine the level of mobilization. Finally, the project emphasizes the importance of coordination between the different levels of governance.
Acadie
Nouveau-Brunswick

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.6663
http://journals.openedition.org/etudescaribeennes/6663

Éditeur(s) : Gauthier-villars
Résumé : The submersible-study of four segments of the East Pacific Rise between 17 degrees and 18 degrees 40'S, where the spreading rate is greater than 150 mm/a, allows us to confirm the variability of the accretion processes. The segment between 17 degrees and 17 degrees 30'S shows an intense present-day magmatic activity. The one between 18 degrees 10' and 18 degrees 22'S shows a mainly tectonic activity. The segment between 18 degrees 22' and 18 degrees 37'S is an intermediate stage with an axial graben in which fresh lavas were emplaced by an extremely young eruption. On all the segments the hydrothermal activity exists ranging from shimmering water up to black smokers, It is associated with different stages of animal colonization.
L'étude par le submersible Nautile de quatre segments de la Dorsale Est Pacifique entre 17° et 18°40'S où le taux d'ouverture est de plus de 150 mm/an, permet de confirmer la variabilité des processus de l'accrétion dans le temps et dans l'espace. Le segment compris entre 17° et 17°30'S montre une intense activité magmatique actuelle ou sub-actuelle, celui compris entre 18°10' et 18°22'S montre une activité essentiellement tectonique et celui compris entre 18°22' et 18°37'S une combinaison des deux, le graben d'extension étant partiellement rempli de laves émises lors d'une éruption extrêmement récente. Partout existe une activité hydrothermale, allant de l'émission de fluides moirés à des fumeurs noirs, associée à divers stades de colonisation animale.
Comptes Rendus de l'Academie des Sciences Serie II (1251-8069) (Gauthier-villars), 1994-10 , Vol. 319 , N. 7 , P. 811-818

Droits : Académie des Sciences
http://archimer.ifremer.fr/doc/00183/29458/27840.pdf
http://archimer.ifremer.fr/doc/00183/29458/

Éditeur(s) : HAL CCSD Society for Molecular Biology and Evolution
Résumé : International audience
Vibrio metoecus is the closest relative of Vibrio cholerae, the causative agent of the potent diarrheal disease cholera. Although the pathogenic potential of this new species is yet to be studied in depth, it has been co-isolated with V. cholerae in coastal waters and found in clinical specimens in the USA. We used these two organisms to investigate the genetic interaction between closely related species in their natural environment. The genomes of twenty V. cholerae and four V. metoecus strains isolated from a brackish coastal pond on the US east coast, as well as four clinical V. metoecus strains were sequenced and compared to reference strains. Whole genome comparison shows 86-87% average nucleotide identity (ANI) in their core genes between the two species. On the other hand, the chromosomal integron, which occupies approximately 3% of their genomes, shows higher conservation in ANI between species than any other region of their genomes. The ANI of 93-94% observed in this region is not significantly greater within than between species, meaning that it does not follow species boundaries. V. metoecus does not encode toxigenic V. cholerae major virulence factors, the cholera toxin and toxin co-regulated pilus. However, some of the pathogenicity islands found in pandemic V. cholerae were either present in the common ancestor it shares with V. metoecus, or acquired by clinical and environmental V. metoecus in partial fragments. The virulence factors of V. cholerae are therefore both more ancient and more widespread than previously believed. There is high interspecies recombination in the core genome, which has been detected in 24% of the single-copy core genes, including genes involved in pathogenicity. V. metoecus was six times more often the recipient of DNA from V. cholerae as it was the donor, indicating a strong bias in the direction of gene transfer in the environment.
ISSN: 1759-6653

Droits : http://creativecommons.org/licenses/by/
hal-01264332
http://hal.upmc.fr/hal-01264332
http://hal.upmc.fr/hal-01264332/document
http://hal.upmc.fr/hal-01264332/file/Genome%20Biol%20Evol-2015-Orata-gbe_evv193.pdf
DOI : 10.1093/gbe/evv193

Résumé : In an effort to implement new fishing activities for the small scale fisheries of Reunion Island, a prospecting cruise targeting deep demersal fish (200 to 600 m) was set up on the west coast of Reunion Island in 2000. This project was carried out by the Regional Fishery Committee and the French Institute for the Exploration of the Sea (Ifremer). Large commercial stocks were identified, and numerous professional or recreational fishermen started employing electric winches to exploit these deep resources. However, the deep demersal species are a fragile resource due mainly to low growth rates and late sexual maturation. Due to the rapid increase in fishing pressure, Ifremer was asked to set up a new study and two scientific campaigns were carried out in 2011 (68 fishing trips being conducted with 559 dropline operations). The first cruise was conducted at the same sites, using the same types of fishing gear and methods used in 2000. A marked drop of greater than 90% was observed in the catches of commercial species, together with a decrease of most fish sizes, attesting the overexploitation of these stocks. Only, catches of the small non-commercial shark (Squalus megalops) remained important (50% in number and weight of total catches). The second cruise extended the prospection area to all waters surrounding Reunion Island . The overexploitation was confirmed in the west of Reunion Island, and in to a lesser degree in the north. Yields were better along the east and the south coasts. Concurrently, the efficiency of 2 hook sizes was compared : small hooks caught significantly more fish but of significantly smaller body sizes, resulting in comparable total weight of fish. We conclude that medium size hooks (i.e. type 7/0) have a significant selectivity on the fish size without loss in the global catch yield. Various types of baits were also tested with the flesh of small local pelagic fish species (Selar crumenophtalmus and Decapterus macarellus) appearing to be the most efficient. This study provides helpful indicators for the management of demersal fish stocks in Reunion island, which have been poorly surveyed and poorly regulated until now. However, the total fishing effort, especially from recreational fishermen, remains the most important factor to be quantified.
Dans la perspective de diversifier la Petite Pêche réunionnaise, une campagne de prospection des stocks de poissons démersaux profonds (200 à 600 m) avait été réalisée en 2000 par le Comité Régional des Pêches Maritimes (CRPM) et l'Institut Français de Recherche pour L'Exploitation de la Mer (Ifremer) dans l'ouest de l'île de La Réunion. Elle a montré l'existence de stocks commercialement intéressants et de nombreux pêcheurs, professionnels et plaisanciers se sont équipés en moulinets électriques pour exploiter ces ressources profondes. Cependant les poissons démersaux profonds représentent une ressource fragile du fait, notamment, de leur croissance lente et de leur maturité sexuelle tardive. Aussi, face à cette augmentation rapide de la pression de pêche, Ifremer a été sollicité pour mener une nouvelle étude ; et deux nouvelles campagnes expérimentales ont été réalisées en 2011 (68 marées ayant permis la réalisation de 559 filages). La première campagne a repris les mêmes sites de pêche, le même matériel et la même méthodologie qu’en 2000. Elle montre que les rendements en espèces commerciales ont diminué de façon très nette (plus de 90%) ainsi que la taille de certaines espèces, indicateurs caractéristiques d'une surexploitation des stocks. Seules les captures de requins zépines (Squalus megalops,) non commercialisées à La Réunion, restent comparables à celles de 2000 avec la moitié des captures totales. La 2e campagne a étendu la prospection à tout le tour de l'île. La surpêche (baisse des rendements et des tailles de poisson) est confirmée dans l'ouest et à un moindre degré sur la côte nord. Les rendements sont meilleurs dans l'est et le sud. Parallèlement, 2 tailles d'hameçons ont été comparées : les petits hameçons capturent un nombre significativement plus élevé de poissons par filage, mais de tailles plus petites, ce qui se traduit par un poids global comparable. Les hameçons de taille moyenne (type 7/0) ont donc une sélectivité significative sur la taille des poissons capturés sans nuire au rendement global. Des comparaisons ont aussi porté sur les types d'appât : Les laizes de petits pélagiques locaux (pêche-cavale et bancloche) se révèlent les plus efficaces et les plus sélectives vis-à-vis des espèces commerciales. Cette étude fournit des indicateurs utiles à la gestion des stocks démersaux jusqu'ici peu étudiés et peu encadrés. Mais la grande inconnue reste l'effort de pêche total sur cette ressource et notamment celui des pêcheurs plaisanciers.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00098/20902/18837.pdf
DOI:10.13155/20902
http://archimer.ifremer.fr/doc/00098/20902/

Éditeur(s) : HAL CCSD
Résumé : International audience
The development of the mine, gas and oil extraction in the Eastern Venezuela (Oriente and Guayana regions) and the Far Eastern (Oriental Siberia) is characterized by the emergence of pioneer small and medium cities during the last fifty years and an emerging process of metropolisation since 2000 (Yakutsk, Ciudad Guayana). In Eastern Venezuela, the urbanization is partially planned, generally “spontaneous”. In Yakutia, dynamics of urbanization is planned. In the both cases, urban dynamics is driven by the exploitation of the natural resources and the immigration. With the collapse of the Soviet Union, some mining towns disappeared in the 1990 and 2000. Since the beginning of the 2010’s mining urban regions are under a double process of territorial integration with Russian Europe and Asia. In Venezuela, small and medium sized cities are growing with the emergence of new mining territories and the exploitation of the Orinoco Belt (extra heavy oil). This article analyses the main territorial dynamics of these small and medium sized cities.
Digital Cities and Spatial Justice

ISBN : 978-84-697-4984-5
hal-01584550
https://hal-amu.archives-ouvertes.fr/hal-01584550

Éditeur(s) : Elsevier
Résumé : The French Guiana transform margin and Demerara abyssal plain have been recently surveyed in the framework of the EXTRAPLAC French Program of extension of the continental shelf (Guyaplac survey, Ifremer-IFP-SHOM-IPEV). Based on the interpretation of some of the data collected during the Guyaplac survey (Simrad-EM12 multibeam bathymetric data, backscatter imagery, and 3.5 kHz profiles), the area can be divided into three morphostructural domains. (1) The western Guiana margin, including a part of the Demerara plateau, an important bathymetric relief prolonging the continental platform off Guiana and Surinam. This domain is bounded by (1a) the NWSE trending northern border of the Demerara plateau which appears quite steep and corresponds to a transform segment of the margin, (1b) the N-S eastern border of the Demerara plateau which corresponds to a divergent segment of the margin. The Demerara plateau shows a segmented morphology, low slope gradients, and a very rough surface (ripples perpendicular to the slope direction). NNW-SSE structural steps seem to correspond to collapses of 100 km long blocs towards the east. Slumps initiate along these directions. The observed rough bathymetry seems to be related to creeping processes. At a greater scale (seismic data), this part of the margin has been totally destabilized (numerous imbricate transparent masses rooted at about 0.5 s.t.w.t.t. below seafloor). The NW-SE trending northern border of the Demerara plateau corresponds to a cliff-like continental slope, probably slightly smoother than other transform margins (Ghana/cote d'Ivoire margin). The N-S eastern border of Demerara plateau is characterized by numerous small-scale imbricate slumps. Some of these failures seem to be emplaced in the prolongation of the NNW-SSE structural steps identified on the Demerara plateau. (2) The eastern Guiana margin corresponds to a NW-SE oriented gullied transform margin segment. The associated continental slope is very steep and characterized by numerous imbricate slumps and related debris flows. Some undulated masses, probably corresponding to creeping sediments or to older mass-wasting events are still imprinted on bathymetry. This transform margin segment is nearly entirely destabilized and eroded. (3) The Demerara abyssal plain. This domain is characterized eastwards by channels belonging to the Amazon turbidite system and westwards, at the foot of Demerara continental slope, by sediment waves probably created by contour currents. To conclude, it seems that there is a strong relationship between the structure (transform and divergent segments) and the emplacement of recurrent slope instabilities. These are probably related to the steepness of the slopes but also to subsidence histories generating in some cases huge deep-seated collapses of the whole margin. Fluid ascents are common everywhere in the area, probably enhancing slope instability. Their origin is not constrained but the black shales or Cretaceous organic-rich layers could be good candidates.
Marine and Petroleum Geology (0264-8172) (Elsevier), 2009-05 , Vol. 26 , N. 5 , P. 711-723

Droits : 2008 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6856.pdf
DOI:10.1016/j.marpetgeo.2008.02.010
http://archimer.ifremer.fr/doc/00000/6856/

Éditeur(s) : HAL CCSD
Résumé : The purpose of this work is to specify the deformation offshore East of Taiwan by characterizing major active faults in particular at the level of the Ryukyu forearc. The major problem associated with the study of this region is that earthquakes are located outside the permanent networks. Consequently, this led to some unprecise earthquake locations limiting tectonic and statistical analyses, and therefore the correct estimation of the seismic hazard. This work is included in the project ANR ACTS (Active Tectonics and Seismic Hazard in Taiwan). To achieve this goal, we worked on three different timescales for which a different localization method has been proposed to obtain a clear image of seismic deformation and highlight major faults offhore East of Taiwan. First, at the scale of the century (from the analysis of a seismicity catalogue with homogeneous magnitude), the instrumental historical earthquakes (1897-2007) show that the Ryukyu margin was affected by 6 earthquakes of magnitude greater than 7 with 4 of them for which the responsible fault is unknown. We propose a method of relative location to relocate the historic events from the time difference of P and S arrival times (Ts-Tp) at each station. The location is obtained by searching for "analogue" earthquakes in the recent instrumental catalogue (1991-2008) for which Ts-Tp at each station is close. This method has been applied to the largest (in terms of magnitude) earthquake ever recorded in Taiwan, the earthquake of June 5, 1920 (M7.7 +/- 0.2). A rupture along the interplate of the Ryukyu subduction with a possible nucleation at the downdip limit of a splay-fault is certainly responsible of this earthquake. Then, at the scale of the decade, the improvement of the method of absolute location based on MAXimum of Intersection of EDT (MAXI, EDT: Equal Differential Time) allows to better extract the erroneous arrival times and prevents the "trade-off" between depth and origin time, and between depth and epicentral position when the azimuthal coverage is low (gap Azimuthal > 180degre). Synthetic tests show the effectiveness of MAXI (using P-wave only) to determine the parameters x, y and z even when the azimuthal gap is important. In the latter case, the quality of the results is dependent on the velocity model to represent the 3D structure of the Earth. We propose an approach involving the use of a 3D a priori P-wave velocity model to locate earthquakes which are lateral and remote to the seismic network. An application to the case of Taiwan and Ecuador validates this approach. Finally, at the level of a few months, the marine geophysical campaign RATS (Ryukyu Arc: Tectonics and Seismology) was conducted in two stages. A passive seismology experiment from July to October, 2008 (RATS1) has been conducted over the forearc of the Ryukyus and then active seismic experiment (refraction and reflection) was conducted in May 2009 in a NNE - SSW line through the Ryukyu margin. These two combined experiments allow improving our knowledge about the crustal structure of the margin. At the level of the forearc, the basement of the forearc is characterized by vertical backstop and a very deformed basis certainly associated with a significant out of sequence deformation. In depth, the downgoing plate is certainly affected by a tear that controls the seismicity in the region of transition between the subduction and collision.
Le but de ce travail est de préciser la déformation en mer à l'est de Taïwan et de notamment caractériser les failles actives majeures en particulier au niveau de l'avant-arc des Ryukyus. Le problème majeur associé à l'étude de cette région est que les séismes sont localisés en dehors des réseaux permanents et que cela conduit à des localisations peu précises limitant les analyses statistiques, tectoniques et donc l'estimation correcte de l'aléa sismique. Ce travail est inclus dans le projet ANR ACTS (Active Tectonics and Seismic Hazard in Taiwan). Pour atteindre cet objectif, nous travaillons à trois échelles de temps différentes pour lesquelles une méthode de localisation différente a été proposée pour obtenir une image précise de la déformation sismique et mettre en évidence les failles majeures en mer à l'est de Taïwan. D'abord, à l'échelle du siècle (à partir de l'analyse d'un catalogue de sismicité homogène en magnitude), les séismes historiques instrumentaux (1897-2007) montrent que la marge des Ryukyus a été affectée par 6 séismes de magnitude supérieure à 7 dont 4 pour lesquels la faille responsable n'est pas connue. Nous proposons une méthode de localisation relative qui permet de relocaliser les évènements historiques à partir des différences de temps d'arrivées P et S (Ts-Tp) à chaque station. La localisation est obtenue en recherchant les séismes analogues dans le catalogue instrumental récent (1991-2008) pour lesquels Ts-Tp à chaque station est proche. Cette méthode a été appliquée au plus gros séisme (en terme de magnitude) jamais enregistré à Taïwan, le séisme du 5 juin 1920 (M7.7 $pm$ 0.2). Ce séisme a certainement pour origine une rupture sur l'interplaque sismogène de la subduction des Ryukyus avec une possible nucléation à la base d'une faille hors-séquence. Ensuite, à l'échelle de la dizaine d'années, l'amélioration de la méthode de localisation absolue du MAXimum d'Intersection EDT (MAXI, EDT: Equal Differential Time) permet de mieux extraire les temps d'arrivées erronés et empêche les "trade-off" entre profondeur et temps d'origine et, entre profondeur et position épicentrale lorsque la couverture azimutale est faible (gap azimutal > 180°). Des tests synthétiques montrent l'efficacité de MAXI (en utilisant les ondes P uniquement) à déterminer les paramètres x, y et z même lorsque le gap azimutal est important. Dans ce dernier cas, la qualité des résultats reste dépendant du modèle de vitesse à représenter la structure 3D de la Terre. Nous proposons une démarche associant l'utilisation d'un modèle de vitesse des ondes P 3D a priori avec la méthode MAXI pour localiser les séismes qui sont latéraux et éloignés du réseau. Une application au cas de Taïwan et en Équateur valide cette approche. Enfin, à l'échelle de quelques mois, la campagne de géophysique marine RATS (Ryukyu Arc: Tectonics and Seismology) a été menée en deux temps. Une expérience de sismologie passive de juillet à octobre 2008 (RATS1) a été menée au-dessus de l'avant-arc des Ryukyus puis une expérience de sismique active (réfraction et réflexion) a été menée en mai 2009 sur une ligne NNE-SSW à travers la marge des Ryukyus. Ces deux expériences combinées permettent d'améliorer notre connaissance de la structure crustale de la marge. Au niveau de l'avant-arc, le socle de l'avant-arc est caractérisé par une extrémité formant un butoir vertical et une base très déformée certainement associée à une importante déformation hors-séquence. En profondeur, la plaque plongeante est certainement affectée par une déchirure qui contrôle la sismicité dans cette région de transition entre la subduction et la collision.
https://tel.archives-ouvertes.fr/tel-00660737

tel-00660737
https://tel.archives-ouvertes.fr/tel-00660737
https://tel.archives-ouvertes.fr/tel-00660737/document
https://tel.archives-ouvertes.fr/tel-00660737/file/Thesis_small.pdf

Éditeur(s) : HAL CCSD BioMed Central
Résumé : [b]Background[/b]: [i]Amblyomma variegatum[/i] and [i]A. hebraeum[/i] are two ticks of veterinary and human health importance in south-east Africa. In Zimbabwe they occupy parapatric (marginally overlapping and juxtaposed) distributions. Understanding the mechanisms behind this parapatry is essential for predicting the spatio-temporal dynamics of Amblyomma spp. and the impacts of associated diseases. It has been hypothesized that exclusive competition between these species results from competition at the levels of male signal reception (attraction-aggregation-attachment pheromones) or sexual competition for mates. This hypothesis predicts that the parapatry described in Zimbabwe could also be present in other countries in the region. [br/][b]Methods[/b]: To explore this competitive exclusion hypothesis we conducted field surveys at the two species' range limits in Mozambique to identify areas of sympatry (overlapping areas) and to study potential interactions (communicative and reproductive interference effects) in those areas. At sympatric sites, hetero-specific mating pairs were collected and inter-specific attractiveness/repellent effects acting at long and short distances were assessed by analyzing species co-occurrences on co-infested herds and co-infested hosts.[br/] [b]Results[/b]: Co-occurrences of both species at sampling sites were infrequent and localized in areas where both tick and host densities were low. At sympatric sites, high percentages of individuals of both species shared attachment sites on hosts and inter-specific mating rates were high. Although cross-mating rates were not significantly different for[i] A. variegatum[/i] and [i]A. hebraeum[/i] females, attraction towards hetero-specific males was greater for [i]A. hebraeum[/i] females than for A. variegatum females and we observed small asymmetrical repellent effects between males at attachment sites.[br/][b]Conclusions[/b]: Our observations suggest near-symmetrical reproductive interference between [i]A. variegatum[/i] and [i]A. hebraeum[/i], despite between-species differences in the strength of reproductive isolation barriers acting at the aggregation, fixation and partner contact levels. Theoretical models predict that sexual competition coupled with hybrid inviability, greatly reduces the probability of one species becoming established in an otherwise suitable location when the other species is already established. This mechanism can explain why the parapatric boundary in Mozambique has formed within an area of low tick densities and relatively infrequent host-mediated dispersal events.
ISSN: 1756-3305

hal-01220744
https://hal.archives-ouvertes.fr/hal-01220744
https://hal.archives-ouvertes.fr/hal-01220744/document
https://hal.archives-ouvertes.fr/hal-01220744/file/2015%20Bournez%20Parasites%20%26%20Vectors_%7B365AAFF5-7041-480B-9B77-9CD0485A9B72%7D.pdf
DOI : 10.1186/s13071-015-1116-7