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A common deep source for upper-mantle upwellings below the Ibero-western Maghreb region from teleseismic P-wave travel-time tomography
No full textUpper-mantle upwellings are often invoked as the cause of Cenozoic volcanism in the Ibero-western Maghreb region. However, their nature, geometry and origin are unclear. This study takes advantage of dense seismic networks, which cover an area extending from the Pyrenees in the north to the Canaries in the south, to provide a new high-resolution P-wave velocity model of the upper-mantle and topmost lower-mantle structure. Our images show three subvertical upper-mantle upwellings below the Canaries, the Atlas Ranges and the Gibraltar Arc, which appear to be rooted beneath the upper-mantle transition zone (MTZ). Two other mantle upwellings beneath the eastern Rif and eastern Betics surround the Gibraltar subduction zone. We propose a new geodynamic model in which narrow upper-mantle upwellings below the Canaries, the Atlas Ranges and the Gibraltar Arc rise from a laterally-propagating layer of material below the MTZ, which in turn is fed by a common deep source below the Canaries. In the Gibraltar region, the deeply rooted upwelling interacts with the Gibraltar slab. Quasi-toroidal flow driven by slab rollback induces the hot mantle material to flow around the slab, creating the two low-velocity anomalies below the eastern Betics and eastern Rif. Our results suggest that the Central Atlantic plume is a likely source of hot mantle material for upper-mantle upwellings in the Ibero-western Maghreb region
Thermal Nature of Mantle Upwellings Below the Ibero‐Western Maghreb Region Inferred From Teleseismic Tomography
Get PDFIndependent models of P wave and S wave velocity anomalies in the mantle derived from seismic tomography help to distinguish thermal signatures from those of partial melt, volatiles, and compositional variations. Here we use seismic data from SW Europe and NW Africa, spanning the region between the Pyrenees and the Canaries, in order to obtain a new S‐SKS relative arrival‐time tomographic
model of the upper mantle below Iberia, Western Morocco, and the Canaries. Similar to previous P wave tomographic results, the S wave model provides evidence for (1) subvertical upper‐mantle
low‐velocity structures below the Canaries, Atlas Ranges, and Gibraltar Arc, which are interpreted as mantle upwellings fed by a common lower‐mantle source below the Canaries; and (2) two low‐velocity anomalies below the eastern Rif and Betics that we interpret as the result of the interaction between quasi‐toroidal mantle flow induced by the Gibraltar slab and the mantle upwelling behind it. The analysis of teleseismic P wave and S wave arrival‐time residuals and the conversion of the low‐velocity anomalies to temperature variations suggest that the upwellings in the upper mantle below the Canaries, Atlas Ranges, and Gibraltar Arc system may be solely thermal in nature, with temperature excesses in the range
~100–350 °C. Our results also indicate that local partial melting can be present at lithospheric depths, especially below the Atlas Ranges. The locations of thermal mantle upwellings are in good agreement with those of thinned lithosphere, moderate to high heat‐flow measurements, and recent magmatic
activity at the surface
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Ocean bottom seismic noise : applications for the crust knowledge, interaction ocean-atmosphere and instrumental behaviour
No full textTese de doutoramento, Ciências Geofísicas e da Geoinformação (Geofisíca), Universidade de Lisboa, Faculdade de Ciências, 2014The seismic observation by long deployment experiments in ocean domain is a great technological challenge, with advancements only having been obtained in the last decade. The number of available instruments is still small and the number of missions successfully carried out remains low. Therefore, unlike land observation, seismic acquisition in the ocean seafloor is in an experimental phase and part of a learning process. In particular, the interaction of the sensor with the water environment has implications and applications that have only recently begun to be explored. In this PhD thesis we intend to use the continuous recording data produced by 24 broad-band (BB) ocean bottom seismometers (OBS), deployed in the Gulf of Cádiz in the context of the NEAREST project (September 2007 – August 2008), to understand the functioning of this type of equipment, the environmental conditions that control the observed noise and the effects of the sensor coupling. Sea floor records have a basic characteristic that makes them different from land records: the sensor’s interaction with the surrounding sea water (e.g. Webb, 1998). Sensors will respond to water movement and pressure variations, which does not happen with land sensors and, in most cases, they are deployed at locations with non-consolidated sediments that dramatically affect the quality of the seismic signal. The future growth of seismic observation at the bottom of the ocean, which is a fundamental complement to land observation, requires that all these mechanisms that affect the seismic records of an OBS are characterized in the best possible way, leading to better equipment design and better conception of observation campaigns, in line with the intended objectives. The continuous acquisition of seismic data by land stations, which is possible today due to the evolution of communications and recording systems, enables us to accumulate an enormous volume of data of which earthquakes are a tiny part, less than 5 % of the recorded data for one day. The remaining 95%, which is rejected in the normal operation of a seismic network, has been receiving attention from researchers in several domains. In particular, when the noise sources are distributed homogeneously (or almost) around a couple of stations it is possible to show that the noise correlation function (NCF) represents the Green function of seismic propagation (in Shapiro and Campillo, 2004, Sabra et al., 2005). This theorem has led to a great number of applications: i) Seismic ambient noise as an efficient tool for seismic tomography (for example: Stehly et al., 2009; Villaseñor et al., 2007, Graça et al., 2013); ii) detection of anomalies in seismic records (e.g., Stehly et al., 2007); iii) variations in superficial structure with time (e.g., Brenguier et al., 2008). Studies of noise sources have increased in the research community, but studies carried out in ocean domains are scarce and joint land-ocean are even more rare. In this thesis, we intend to use the continuous seismic recording, mainly the ambient noise component, to extract information related with: i) shallow crustal structure; ii) conditions of sensor coupling; iii) clock drifts of the acquisition systems; iv) meteorological and oceanographic environmental noise sources. For this purpose it was crucial to implement new methodologies and to adapt current procedures in land records. At the end of these studies we hope to be able to make some recommendations regarding: i) conception and design of BB OBS; ii) interpretation of seismic signals recorded at the ocean bed; iii) planning of future campaigns of long deployment seismic experiments.A observação sísmica de longa duração, em ambiente marinho, representa um grande desafio tecnológico e apenas nas últimas décadas foram obtidos avanços significativos. Os instrumentos disponíveis são limitados e o número de missões com sucesso é ainda reduzido. Ao contrário da observação terrestre, a aquisição sísmica no fundo do oceano encontra-se numa fase experimental e em contínuo processo de aprendizagem. Em particular, a interação do sensor com o ambiente marítimo tem implicações e aplicações que só recentemente começaram a ser exploradas. Nesta tese de doutoramento, pretendemos usar os dados registados em 24 estações sísmicas de banda larga (BB), de fundo oceânico (OBS), implantadas no Golfo de Cádiz, no âmbito do projeto NEAREST (Setembro de 2007- Agosto de 2008), para melhor compreender o funcionamento deste tipo de equipamento, as condições ambientais que controlam o ruído observado e os efeitos de acoplamento do sensor. Os registos no fundo do mar têm uma característica básica que os diferencia dos de terra: a interação do sensor com a água do mar circundante (Webb, 1998). O sensor irá responder ao movimento da água e às variações de pressão, fenómeno que não acontece nos sensores terrestres, e o facto de estar instalado em áreas de sedimentos não consolidados também afeta dramaticamente a qualidade do sinal sísmico. O desenvolvimento da observação sísmica no fundo oceânico, é fundamental para completar a observação em terra e exige que todos os mecanismos que afectam os registos sísmicos de um OBS sejam caracterizados o melhor possível, para aprimorar a concepção dos equipamentos e de uma melhor concepção de campanhas de observação, em função dos objectivos a alcançar. As redes de estações sísmicas terrestres de registo contínuo, permitidas hoje pela evolução das comunicações e dos sistemas de aquisição, permitem acumular um volume enorme de dados, dos quais os eventos sísmicos são apenas uma pequena parte, menos de 5% dos dados registados diariamente. Os remanescentes 95%, os quais eram anteriormente rejeitados, recebem actualmente especial atenção dos investigadores das diferentes áreas da sismologia. Em particular, quando as fontes de ruído, são distribuídas de forma homogénea (ou quase), em redor de um par de estações, é possível demonstrar que a função de correlação do ruído (NCF), representa a “Green function” da propagação sísmica (em Shapiro e Campillo, 2004; Sabra et al., 2005). Este teorema tem levado a um grande número de aplicações : i) Ruído sísmico ambiental como uma ferramenta eficiente para tomografia sísmica (por exemplo: Stehly et al., 2009; Villaseñor et al., 2007; Graça et al., 2013); ii) detecção de sinais anómalos nos registos sísmicos (v.g. Stehly et al., 2007); iii) variações na estrutura de propagação com o tempo (por exemplo, Brenguier et al, 2008). Os estudos sobre fontes de ruído terrestre aumentaram na comunidade científica, mas no domínio oceânico são, ainda, escassos. Nesta tese, pretende-se usar o registo contínuo dos dados sísmicos, principalmente a componente de ruído ambiente, para extrair informações relacionadas com: i) estrutura de crosta superficial e sua reologia; ii) acoplamento do sensor; iii) derivas temporais no relógio dos sistemas de aquisição; iv) características das fontes de ruído ambiental, meteorológico e oceanográfico. Para isso, é crucial implementar novas metodologias e adaptar os procedimentos realizados nos registos terrestres. No final deste estudo, pretende-se formular algumas recomendações sobre: i) concepção e desenho de OBS BB; ii ) a interpretação dos inúmeros sinais sísmicos registados no leito do oceano, iii) o planeamento de futuras campanhas de longa duração
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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