Intraplate seismicity across the Cape Verde swell: a contribution from a temporary seismic network

We present an analysis and characterization of the regional seismicity recorded by a temporary broadband seismic network deployed in the Cape Verde archipelago between November 2007 and September 2008. The detection of earthquakes was based on spectrograms, allowing the discrimination from low-frequency volcanic signals, resulting in 358 events of which 265 were located, the magnitudes usually being smaller than 3. For the location, a new 1-D P-velocity model was derived for the region showing a crust consistent with an oceanic crustal structure. The seismicity is located mostly offshore the westernmost and geologically youngest areas of the archipelago, near the islands of Santo Antao and Sao Vicente in the NW and Brava and Fogo in the SW. The SW cluster has a lower occurrence rate and corresponds to seismicity concentrated mainly along an alignment between Brava and the Cadamosto seamount presenting normal faulting mechanisms. The existence of the NW cluster, located offshore SW of Santo Antao, was so far unknown and concentrates around a recently recognized submarine cone field; this cluster presents focal depths extending from the crust to the upper mantle and suggests volcanic unrest No evident temporal behaviour could be perceived, although the events tend to occur in bursts of activity lasting a few days. In this recording period, no significant activity was detected at Fogo volcano, the most active volcanic edifice in Cape Verde. The seismicity characteristics point mainly to a volcanic origin. The correlation of the recorded seismicity with active volcanic structures agrees with the tendency for a westward migration of volcanic activity in the archipelago as indicated by the geologic record. (C) 2014 Elsevier B.V. All rights reserved.

Simulation of rectifier voltage malfunction on OWECS, four-level converter, HVDC light link: Smart grid context tool

This paper presents a model for the simulation of an offshore wind system having a rectifier input voltage malfunction at one phase. The offshore wind system model comprises a variable-speed wind turbine supported on a floating platform, equipped with a permanent magnet synchronous generator using full-power four-level neutral point clamped converter. The link from the offshore floating platform to the onshore electrical grid is done through a light high voltage direct current submarine cable. The drive train is modeled by a three-mass model. Considerations about the smart grid context are offered for the use of the model in such a context. The rectifier voltage malfunction domino effect is presented as a case study to show capabilities of the model. (C) 2015 Elsevier Ltd. All rights reserved.

Evidências geomorfológicas de alguns processos responsáveis pela evolução quaternária do canhão de Setúbal

The deep submarine valley near Setúbal that connects the continental platform to the Tagus Abyssal Plain is a submarine canyon of the type commonly knows as Gouf. In this article we try to show the tectonic influence in its formation and in the installation of its submarine hydrographic net. Some indirect evidences of erosive processes responsible for the formation of typical submarine forms of canyons are analysed based in the interpretation of the batimetric map. Finally, we try to give a brief idea of the evolution of this canyon based on the knowledge that is accepted for the area where he belongs.

Simulation of offshore wind system with three-level converters: HVDC power transmission in cloud scope

This paper is on a simulation for offshore wind systems in deep water under cloud scope. The system is equipped with a permanent magnet synchronous generator and a full-power three-level converter, converting the electric energy at variable frequency in one at constant frequency. The control strategies for the three-level are based on proportional integral controllers. The electric energy is injected through a HVDC transmission submarine cable into the grid. The drive train is modeled by a three-mass model taking into account the resistant stiffness torque, structure and tower in the deep water due to the moving surface elevation. Conclusions are taken on the influence of the moving surface on the energy conversion. © IFIP International Federation for Information Processing 2015.

Aplicação da teoria das opções reais em análise de projetos estratégicos: um estudo de caso sobre o valor da opção de prosseguir com os investimentos no programa de desenvolvimento de submarinos da Marinha do Brasil

Dissertação de mestrado em Estudos de Gestão

Simulation of a rectifier malfunction on a offshore wind system with HVDC transmission

A new integrated mathematical model for the simulation of an offshore wind system having a rectifier input voltage malfunction at one phase is presented in this paper. The mathematical model considers an offshore variable-speed wind turbine on a floating platform, equipped with a permanent magnet synchronous generator using full-power three-level converter to inject energy into the electric network, through a high voltage direct current transmission submarine cable. The model for the drive train is a discrete three mass, incorporating the dynamic of the moving surface. A case study is presented to access conclusion about the malfunction.

Depleted arc volcanism in the Alboran Sea and shoshonitic volcanism in Morocco: geochemical and isotopic constraints on Neogene tectonic processes

Samples of volcanic rocks from Alboran Island, the Alboran Sea floor and from the Gourougou volcanic centre in northern Morocco have been analyzed for major and trace elements and Sr-Nd isotopes to test current theories on the tectonic geodynamic evolution of the Alboran Sea. The Alboran Island samples are low-K tholeiitic basaltic andesites whose depleted contents of HFS elements (similar to0.5xN-MORB), especially Nb (similar to0.2xN-MORB), show marked geochemical parallels with volcanics from immature intra-oceanic arcs and back-arc basins. Several of the submarine samples have similar compositions, one showing low-Ca boninite affinity. Nd-143/Nd-144 ratios fall in the same range as many island-arc and back-arc basin samples, whereas Sr-87/Sr-86 ratios (on leached samples) are somewhat more radiogenic. Our data point to active subduction taking place beneath the Alboran region in Miocene times, and imply the presence of an associated back-arc spreading centre. Our sea floor suite includes a few more evolved dacite and rhyolite samples with (Sr-87/Sr-86)(0) up to 0.717 that probably represent varying degrees of crustal melting. The shoshonite and high-K basaltic andesite lavas from Gourougou have comparable normalized incompatible-element enrichment diagrams and Ce/Y ratios to shoshonitic volcanics from oceanic island arcs, though they have less pronounced Nb deficits. They are much less LIL- and LREE-enriched than continental arc analogues and post-collisional shoshonites from Tibet. The magmas probably originated by melting in subcontinental lithospheric mantle that had experienced negligible subduction input. Sr-Nd isotope compositions point to significant crustal contamination which appears to account for the small Nb anomalies. The unmistakable supra-subduction zone (SSZ) signature shown by our Alboran basalts and basaltic andesite samples refutes geodynamic models that attribute all Neogene volcanism in the Alboran domain to decompression melting of upwelling asthenosphere arising from convective thinning of over-thickened lithosphere. Our data support recent models in which subsidence is caused by westward rollback of an eastward-dipping subduction zone beneath the westemmost Mediterranean. Moreover, severance of the lithosphere at the edges of the rolling-back slab provides opportunities for locally melting lithospheric mantle, providing a possible explanation for the shoshonitic volcanism seen in northern Morocco and more sporadically in SE Spain. (C) 2004 Elsevier B.V. All rights reserved.

Oceanic intraplate volcanoes exposed: Example from seamounts accreted in Panama

Two Paleogene ocean islands are exposed in the Azuero Peninsula, west Panama, within sequences accreted in the early-Middle Eocene. A multidisciplinary approach involving litho-logic mapping, paleontological age determinations, and petrological study allows reconstruction of the stratigraphy and magmatic evolution of one of these intraplate oceanic volcanoes. From base to top, the volcano's structure comprises submarine basaltic lava flows locally interlayered with hemipelagic sediments, basaltic breccias, shallow-water limestones, and subaerial basaltic lava. Gabbros and basaltic dikes were emplaced along a rift zone of the island. Geochemical trends of basaltic lavas include decreased Mg# {[Mg/(Mg + Fe)] * 100} and, with time, increased incompatible element contents thought to be representative of many poorly documented intraplate volcanoes in the Pacific. Our results show that, in addition to deep drilling, the roots of oceanic islands can be explored through studies of accreted and subaerially exhumed oceanic sequences.

Ra isotopes and Rn as a tool for the water management resources: the Alberquillas aquifer (Málaga-Granada)

The aim of this project is to evaluate the importance of submarine groundwater discharge sector in order to improve the water balance in Málaga-Granada region. The approach of this study arose from the the geology and the aquifers that indicate that there could be some discharge to the sea between Maro (Málaga) and Almuñécar (Granada) and the Andalusian’s Government and its Water Agence were really interested in evaluating it because there is a lot of population and few water available and the magnitude of groundwater discharge has generated controversy. Is well known that water is a scarce resource in this area and it’s very important for the society and for the environment. The legislation, the water policies, the knowledge of the aquifer and the geology, the water dynamics, the land use and the water perception in the society might help the management of this resource not just in Andalusia but in all the Mediterranean basin. The main objective is to evaluate the submarine groundwater discharge from the Alberquillas Aqufier to the sea by measuring 222Rn and Ra isotopes. Specific objectives have been established to achieve the main objective: A) Reveal the importance of water resources in the Mediterranean basin; B) Learn radiometric techniques for the study of groundwater discharge to the sea; C) Learn of sampling techniques of water samples for the measurement of Ra and Rn; D) Learn the techniques for measuring Ra (RaDeCC) and Rn (RAD7); E) Interpretation and discussion of results. During this semester, and in addition of the present study in Málaga- Granada region, the author has participated in the initial phase (sampling, analysis and interpretation of preliminary results) of other research projects focused on the study of submarine groundwater discharges through the use of Ra isotopes and 222Rn. These studies have been developed in different areas, including Alt Empordà (Roses and Sant Pere Pescador), Maresme with CMIMA’s group (Mediterranean Center for Marine and Environmental Research), Delta de l’Ebre, Peñíscola and Mallorca with the IMEDEA’s group (Mediterranean Institute for Advanced Studies).

Spatio-temporal variations in reproductive patterns and population structure of Pasiphaea multidentata (Decapoda: Caridea) in the Blanes canyon and adjacent margin, North-western Mediterranean Sea

The bathyal faunal communities of the NW Mediterranean slopes have been studied consistently in the last two decades, with a special focus on population structure, trophic dynamics and benthopelagic coupling of commercial deep-sea decapod crustaceans and fishes (reviewed in Sardà et al. 2004) and associated species (Cartes and Sardà, 1993; Company and Sardà, 1997, 2000; Cartes et al., 2001; Company et al., 2001, 2003, 2004). One of the major topographic features in the North-western Mediterranean slope is the presence of submarine canyons. Canyons play a major role in funnelling energy and organic matter from the shelf to bathyal and abyssal depths (Puig et al., 2000), but the implications of this enhanced organic supply in the deep-sea benthic communities is still mostly unknown. Trophic supply can follow two major pathways – vertical deposition in the water column (Billett et al., 1983; Baldwin et al., 1998; Lampitt et al., 2001) or down-slope advection on the margins (Puig et al., 2001; Bethoux et al., 2002; Canals et al., 2006) – and can be a limiting factor in the deep-sea, being especially important in the oligotrophic Mediterranean Sea (Sardà et al., 2004). Differences in the quantity, quality and timing of organic matter input to the deep seafloor have been used to explain patterns of biomass and abundance in benthic communities (Levin et al., 1994; Gooday & Turley, 1990; Billett et al., 2001; Galéron et al., 2001; Puig et al., 2001; Gage, 2003) as well as other biological process and in particular the existence of seasonal reproduction (Tyler et al., 1994; Company et al., 2004 (MEPS). Reproduction is a highly energetic process tightly linked to food availability and quality.

Autonomous underwater vehicle control using reinforcement learning policy search methods

Autonomous underwater vehicles (AUV) represent a challenging control problem with complex, noisy, dynamics. Nowadays, not only the continuous scientific advances in underwater robotics but the increasing number of subsea missions and its complexity ask for an automatization of submarine processes. This paper proposes a high-level control system for solving the action selection problem of an autonomous robot. The system is characterized by the use of reinforcement learning direct policy search methods (RLDPS) for learning the internal state/action mapping of some behaviors. We demonstrate its feasibility with simulated experiments using the model of our underwater robot URIS in a target following task

Biotic effects of the Chicxulub impact, K-T catastrophe and sea level change in Texas

Biotic effects of the Chicxulub impact, the K-T event and sea level change upon planktic foraminifera were evaluated in a new core and outcrops along the Brazos River, Texas, about 1000 km from the Chicxulub impact crater on Yucatan, Mexico. Sediment deposition occurred in a middle neritic environment that shallowed to inner neritic depths near the end of the Maastrichtian. The sea level fall scoured submarine channels, which were infilled by a sandstone complex with reworked Chicxulub impact spherules and clasts with spherules near the base. The original Chicxulub impact ejecta layer was discovered 45-60 cm below the sandstone complex, and predates the K-T mass extinction by about 300,000 years. Results show that the Chicxulub impact caused no species extinctions or any other significant biotic effects. The subsequent sea level fall to inner neritic depth resulted in the disappearance of all larger (>150 mu m) deeper dwelling species creating a pseudo-mass extinction and a survivor assemblage of small surface dwellers and low oxygen tolerant taxa. The K-T boundary and mass extinction was identified 40-80 cm above the sandstone complex where all but some heterohelicids, hedbergellids and the disaster opportunistic guembelitfids went extinct, coincident with the evolution of first Danian species and the global delta(13)C shift. These data reveal that sea level changes profoundly influenced marine assemblages in near shore environments, that the Chicxulub impact and K-T mass extinction are two separate and unrelated events, and that the biotic effects of this impact have been vastly overestimated. (C) 2008 Elsevier B.V. All rights reserved.

Análisis multidisciplinar del fenómeno sismo-volcánico de El Hierro (julio 2011)

La erupción volcánica submarina de La Restinga (10 de octubre) ha permitido, por primera vez, poner en marcha el Plan Especial de Protección Civil y Atención de Emergencias por Riesgo Volcánico en la Comunidad Autónoma de Canarias. En este proyecto se ha realizado un análisis multidisciplinar de los principales elementos que han estado involucrados en la gestión de la crisis y sus repercusiones sociales, económicas y ambientales. Los resultados indican que, hoy en día, se cuenta con los medios necesarios para realizar la detección temprana y el seguimiento de procesos similares que tengan lugar en el Archipiélago pero, no obstante, sería necesario actualizar el presente Plan PEVOLCA, debido a las deficiencias detectadas. Estas deficiencias, además de afectar a la gestión del fenómeno sismo-volcánico, han provocado que se tomasen medidas de protección civil que han generado grandes repercusiones sociales y económicas en la Isla. Respecto a las consecuencias ambientales en la Reserva Marina de Punta La Restinga-Mar de Las Calmas se prevé una recuperación a corto plazo, siempre que se apliquen las medidas necesarias.

Biogeochemical evolution of a marine shore tailings deposit during bioremediation

Summary : Mining activities produce enormous amounts of waste material known as tailings which are composed of fine to medium size particles. These tailings often contain sulfides, which oxidation can lead to acid and metal contamination of water; therefore they need to be remediated. In this work a tailings bioremediation approach was investigated by an interdisciplinary study including geochemistry, mineralogy and microbiology. The aim of the work was to study the effect of the implementation of wetland above oxidizing tailings on the hydrogeology and the biogeochemical element cycles, and to assess the system evolution over time. To reach these goals, biogeochemical processes occurring in a marine shore tailings deposit were investigated. The studied tailings deposit is located at the Bahìa de Ite, Pacific Ocean, southern Peru, where between 1940 and 1996 the tailings were discharged from the two porphyry copper mines Cuajone and Toquepala. After the end of deposition, a remediation approach was initiated in 1997 with a wetland implementation above the oxidizing tailings. Around 90% of the tailings deposits (total 16 km2) were thus remediated, except the central delta area and some areas close to the shoreline. The multi-stable isotope study showed that the tailings were saturated with fresh water in spite of the marine setting, due to the high hydraulic gradient resulting from the wetland implementation. Submarine groundwater discharge (SGD) was the major source of SO4 2-, C1-, Na+, Fe2+, and Mn2+ input into the tailings at the original shelf-seawater interface. The geochemical study (aquatic geochemistry and X-Ray diffraction (XRD) and sequential extractions from the solid fraction) showed that iron and sulfur oxidation were the main processes in the non-remediated tailings, which showed a top a low-pH oxidation zone with strong accumulation of efflorescent salts at the surface due to capillary upward transport of heavy metals (Fe, Cu, Zn, Mn, Cd, Co, and Ni) in the arid climate. The study showed also that the implementation of the wetland resulted in very low concentrations of heavy metals in solution (mainly under the detection limit) due to the near neutral pH and more reducing conditions (100-150 mV). The heavy metals, which were taken from solution, precipitated as hydroxides and sulfides or were bound to organic matter. The bacterial community composition analysis by Terminal Restriction Fragment Length Polymorphism (T-RFLP) and cloning and sequencing of 16S rRNA genes combined with a detailed statistical analysis revealed a high correlation between the bacterial distribution and the geochemical variables. Acidophilic autotrophic oxidizing bacteria were dominating the oxidizing tailings, whereas neutrophilic and heterotrophic reducing bacteria were driving the biogeochemical processes in the remediated tailings below the wetland. At the subsurface of the remediated tailings, an iron cycling was highlighted with oxidation and reduction processes due to micro-aerophilic niches provided by the plant rhizosphere in this overall reducing environment. The in situ bioremediation experiment showed that the main parameter to take into account for the effectiveness was the water table and chemistry which controls the system. The constructed remediation cells were more efficient and rapid in metal removal when saturation conditions were available. This study showed that the bioremediation by wetland implementation could be an effective and rapid treatment for some sulfidic mine tailings deposits. However, the water saturation of the tailings has to be managed on a long-term basis in order to guarantee stability. Résumé : L'activité minière produit d'énormes quantités de déchets géologiques connus sous le nom de « tailings » composées de particules de taille fine à moyenne. Ces déchets contiennent souvent des sulfures dont l'oxydation conduit à la formation d'effluents acides contaminés en métaux, d'où la nécessité d'effectuer une remédiation des sites de stockage concernés. Le but de ce travail est dans un premier temps d'étudier l'effet de la bio-remédiation d'un dépôt de tailings oxydés sur l'hydrogéologie du système et les cycles biogéochimiques des éléments et en second lieu, d'évaluer l'évolution du processus de remédiation dans le temps. Le site étudié dans ce travail est situé dans la Bahía de Ite, au sud du Pérou, au bord de l'Océan Pacifique. Les déchets miniers en question sont déposés dans un environnement marin. De 1940 à 1996, les déchets de deux mines de porphyre cuprifère - Cuajone et Toquepala - ont été acheminés sur le site via la rivière Locumba. En 1997, une première remédiation a été initiée avec la construction d'une zone humide sur les tailings. Depuis, environ 90% de la surface du dépôt (16 km2) a été traité, les parties restantes étant la zone centrale du delta du Locumba et certaines zones proches de la plage. Malgré la proximité de l'océan, les études isotopiques menées dans le cadre de ce travail ont montré que les tailings étaient saturés en eau douce. Cette saturation est due à la pression hydraulique résultant de la mise en place des zones humides. Un écoulement d'eau souterrain sous-marin a été à détecté à l'interface entre les résidus et l'ancien fond marin. En raison de la géologie locale, il constitue une source d'entrée de SO4 2-, Cl-, Na+, FeZ+, et Mn2+ dans le système. L'analyse de la géochimie aquatique, la Diffraction aux Rayons X (XRD) et l'extraction séquentielle ont montré que l'oxydation du fer et .des sulfures est le principal processus se produisant dans les déchets non remédiés. Ceci a entraîné le développement d'une zone d'oxydation à pH bas induisant une forte accumulation des sels efflorescents, conséquence de la migration capillaire des métaux lourds (Fe, Cu, Zn, Mn, Cd, Co et Ni) de la solution vers la surface dans ce climat aride. Cette étude a montré également que la construction de la zone humide a eu comme résultats une précipitation des métaux dans des phases minérales en raison du pH neutre et des conditions réductrices (100-150mV). Les métaux lourds ont précipité sous la forme d'hydroxydes et de sulfures ou sont adsorbés à la matière organique. L'analyse de la composition de la communauté bactérienne à l'aide la technique T-RFLP (Terminal Restriction Fragment Length Polymorphism) et par le clonage/séquençage des gènes de l'ARNr 16S a été combinée à une statistique détaillée. Cette dernière a révélé une forte corrélation entre la distribution de bactéries spécifiques et la géochimie : Les bactéries autotrophes acidophiles dominent dans les déchets oxydés non remédiés, tandis que des bactéries hétérotrophes neutrophiles ont mené les processus microbiens dans les déchets remédiés sous la zone humide. Sous la surface de la zone humide, nos analyses ont également mis en évidence un cycle du fer par des processus d'oxydoréduction rendus possibles par la présence de niches micro-aérées par la rhizosphère dans cet environnement réducteur. L'expérience de bio-remédiation in situ a montré que les paramètres clés qui contrôlent l'efficacité du traitement sont le niveau de la nappe aquifère et la chimie de l'eau. Les cellules de remédiation se sont montrées plus efficaces et plus rapides lorsque le système a pu être saturé en eau. Finalement, cette étude a montré que la bio-remédiation de déchets miniers par la construction de zones humides est un moyen de traitement efficace, rapide et peu coûteux. Cependant, la saturation en eau du système doit être gérée sur le long terme afin de garantir la stabilité de l'ensemble du système.

Global mass wasting during the Middle Ordovician: Meteoritic trigger or plate-tectonic environment ?

Mass wasting at continental margins on a global scale during the Middle Ordovician has recently been related to high meteorite influx. Although a high meteorite influx during the Ordovician should not be neglected, we challenge the idea that mass wasting was mainly produced by meteorite impacts over a period of almost 10 Ma. Having strong arguments against the impact-related hypothesis, we propose an alternative explanation, which is based on a re-evaluation of the mass wasting sites, considering their plate-tectonic distribution and the global sea level curve. A striking and important feature is the distribution of most of the mass wasting sites along continental margins characterised by periods of magmatism, terrane accretion and continental or back-arc rifting, respectively, related to subduction of oceanic lithosphere. Such processes are commonly connected with seismic activity causing earthquakes, which can cause downslope movement of sediment and rock. Considering all that, it seems more likely that most of this mass wasting was triggered by earthquakes related to plate-tectonic processes, which caused destabilisation of continental margins resulting in megabreccias and debris flows. Moreover, the period of mass wasting coincides with sea level drops during global sea level lowstand. In some cases, sea level drops can release pore-water overpressure reducing sediment strength and hence promoting instability of sediment at continental margins. Reduced pore-water overpressure can also destabilise gas hydrate-bearing sediment, causing slope failure, and thus resulting in submarine mass wasting. Overall, the global mass wasting during the Middle Ordovician does not need meteoritic trigger. (C) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.