Seismic Imaging and Salt Tectonics of the Mediterranean Salt Giant in the Central Algerian Basin

The Mediterranean Salt Giant (MSG) is a thick layer of Messinian evaporites (up to 4 km) that is thought to be deposited during an extreme paleo-environmental event known as the Messinian Salinity Crisis (MSC). After decades of research, there is not yet a consensual model explaining the emplacement and the evolution of the MSG. This is due to the absence of samples of the deep offshore MSG. Past scientific drilling operations were limited to the topmost MSG records because of the risks of intersecting zones of hazardous fluids and overpressure linked to evaporites. The European project SALTGIANT, in which the work of this thesis fits into, is dedicated to understanding the formation of the MSG and its implications for the microbial life, the drilling hazards and the geo-economics of the Mediterranean region and the history of oceanography. In that framework, this thesis aims to improve our seismic images of the offshore MSG and to use the new results to update our understanding of the Messinian salt tectonics. This work is focused on the Algerian basin, in the south-western Mediterranean Sea, where the salt was deposited in an already contractional tectonic setting. I compile, reprocess, and interpret legacy academic seismic data acquired in the central Algerian basin. The re-processing is designed to improve as much as possible the salt and pre-salt structures. It relies on an integrated approach combining geophysics and geological interpretation to iteratively build the velocity model. The new results display a better imaging of salt structures and the seismic facies variations. They shed a new light on the tectono-sedimentary evolution of the central Algerian basin, highlighting the presence of seismic fluid indicators evidencing an active fluid circulation in the basin and its margins. Interpretation of the new seismic sections is done following the most recent nomenclature of the MSC seismic markers. New isochores and thickness maps are produced and compared with the spatial distribution of the salt structures. I interpret contractional salt tectonic structures, such as buckle folds, squeezed diapirs and related salt sheets as evidence of regional thick-skinned shortening episodes. I suggest that extensional stage of the salt system (where the deformation is driven by gravity loading) was short-lived, and that many salt structures were driven by contractional tectonic loading during the Plio-Quaternary. I demonstrate that the initial shortening-related salt deformation in the late Messinian was focussed along the Algerian margin and later shifted outward toward the Balearic margin in the Plio-Quaternary. The shifting of the deformation front is interpreted to be a result of the thickening and strengthening of the overburden. The second peak of deformation may have reactivated faults along the Emile-Baudot escarpment with thick-skinned deformation. I also observe a variation in the intensity of the salt deformation along the margin from SW to NE, which I associate to variable tectonic loading applied along the Algerian margin or the pre-shortening distribution of salt. Fluid indicators are imaged within the Plio-Quaternary of the Algerian basin. They could be thermogenic or biogenic gas sourced from the Messinian Upper Unit, or from the pre-salt, migrating through a hydro-fractured salt. The new results also evidence numerous volcanic structures within the Formentera basin. The distribution of this volcanic edifice could affect fluid circulation, resulting in small-wavelength surface HF anomalies observed locally

Hydrodynamic limit for a facilitated exclusion process

International audienceWe study the hydrodynamic limit for a periodic 1-dimensional exclusion process with a dynamical constraint, which prevents a particle at site x from jumping to site x ± 1 unless site x 1 is occupied. This process with degenerate jump rates admits transient states, which it eventually leaves to reach an ergodic component, assuming that the initial macroscopic density is larger than 1 2 , or one of its absorbing states if this is not the case. It belongs to the class of conserved lattice gases (CLG) which have been introduced in the physics literature as systems with active-absorbing phase transition in the presence of a conserved field. We show that, for initial profiles smooth enough and uniformly larger than the critical density 1 2 , the macroscopic density profile for our dynamics evolves under the diffusive time scaling according to a fast diffusion equation (FDE). The first step in the proof is to show that the system typically reaches an ergodic component in subdiffusive time.Nous étudions la limite hydrodynamique d'un système d'exclusion unidimensionnel avec une contrainte dynamique, qui empêche une particule en x de sauter en x ± 1 à moins que x ∓ 1 soit occupé. Ce processus à taux de sauts dégénérés admet des états transients, qu'il finit par quitter pour atteindre une composante ergodique dans le cas où la densité initiale macroscopique est supérieure à 1 2 , ou un de ses états absorbants dans l'autre cas. Ce processus fait partie des gaz conservatifs sur réseau, qui ont été introduits dans la litérature physique comme systèmes présentant une transition de phase active-absorbante en présence d'un champ conservé. Nous montrons que pour des profils initiaux de densité suffisamment réguliers et strictement supérieurs à 1 2 , le profil de densité macroscopique évolue à l'échelle diffusive suivant une équation de diffusion rapide (FDE). La première étape de la preuve consiste à montrer que, typiquement, le système atteint une composante ergodique en temps sous-diffusif

Dynamics of interacting particle systems******

We collect here recent results covering various aspects of the dynamical properties of interacting particle systems. In Section 1 we study the hydrodynamic limit of a facilitated exclusion process. Section 2 evidences a cutoff phenomenon for the mixing time of the weakly asymmetric exclusion process. Section 3 presents a study of the infection time in the Duarte model. Finally, Section 4 presents the study of a front propagation in the FA-If model

Imaging mass‐wasting sliding surfaces within complex glacial deposits along coastal cliffs using geophysics

This study presents a multidisciplinary survey combining geological fieldwork and geophysical data to better constrain the parameters influencing the morphology and behaviour of a retreating coastal cliff. Erosion rates are spatially highly variable and hard to predict because of the manifold parameters acting on them. Among these parameters, rock resistance exerts a paramount influence on cliff retreat. Characterizing the rock resistance distribution along a coastal region requires the mapping of several key subsurface properties including the bulk lithology, faulting, fracturing, or weathering. This is a difficult and expensive task because of the high spatial variability of these factors linked to the spatial complexity of the geology. Geophysical methods can be used to tackle this challenge by quickly providing the 3D visualization and distribution of these parameters within the subsurface. A fast-eroding portion of the Norfolk coast (UK) at West Runton is investigated using a multidisciplinary approach, combining ground-penetrating radar, electrical resistivity tomography (ERT), cone penetration tests, and outcrop studies. The results allowed us to build a 3D geological and geophysical model of a highly complex area of glacial geology. It forms part of a relict glaciotectonic thrust-tip moraine and sand basin sequence. The surfaces interpreted on radar data are associated with strong resistivity contrasts on the ERT data. These contrasts have been attributed to petrophysical variations between the lithological units. The base of the sand basin is marked by a low-permeability clay bed. Its low shear strength is likely to be more susceptible to failure, hereby accelerating the erosion rate of an already fast-eroding sand basin. The resulting model can be used as input for locally constraining the ground parameters in coastal recession and erosion models

Community Detection Based on Modularity and k-Plexes

Abstract(#br)Community identification is of great worth for analyzing the structure or characteristics of a complex network. Many community detection methods have been developed, such as modularity-based optimization models, which are widely used but significantly restricted in “resolution limit”. In this paper, we propose a novel algorithm, called modularity optimization with k -plexes (MOKP), to solve this problem, and this algorithm can identify communities smaller than a scale. The proposed algorithm uses k -plexes to generate community seeds from the whole network and assigns the remaining nodes by modularity optimization. To save computational time, we further propose the improved MOKP algorithm (IMOKP) by reducing the scale of the network before community seeds generation and adjusting rules of nodes assignment. Extensive experimental results demonstrate our proposed algorithms perform better than several state-of-the-art algorithms in terms of accuracy of detected communities on various networks, and can effectively detect small communities in terms of a newly defined index, namely small community level, on multiple networks as well

Structural and Dynamical Patterns on Online Social Networks: the Spanish May 15th Movement as a case study

The number of people using online social networks in their everyday life is continuously growing at a pace never saw before. This new kind of communication has an enormous impact on opinions, cultural trends, information spreading and even in the commercial success of new products. More importantly, social online networks have revealed as a fundamental organizing mechanism in recent country-wide social movements. In this paper, we provide a quantitative analysis of the structural and dynamical patterns emerging from the activity of an online social network around the ongoing May 15th (15M) movement in Spain. Our network is made up by users that exchanged tweets in a time period of one month, which includes the birth and stabilization of the 15M movement. We characterize in depth the growth of such dynamical network and find that it is scale-free with communities at the mesoscale. We also find that its dynamics exhibits typical features of critical systems such as robustness and power-law distributions for several quantities. Remarkably, we report that the patterns characterizing the spreading dynamics are asymmetric, giving rise to a clear distinction between information sources and sinks. Our study represent a first step towards the use of data from online social media to comprehend modern societal dynamics.Comment: 16 pages, 7 figure

The invasome of Salmonella Dublin as revealed by whole genome sequencing

Background Salmonella enterica serovar Dublin is a zoonotic infection that can be transmitted from cattle to humans through consumption of contaminated milk and milk products. Outbreaks of human infections by S. Dublin have been reported in several countries including high-income countries. A high proportion of S. Dublin cases in humans are associated with invasive disease and systemic illness. The genetic basis of virulence in S. Dublin is not well characterized. Methods Whole genome sequencing was applied to a set of clinical invasive and non-invasive S. Dublin isolates from different countries in order to characterize the putative genetic determinants involved in the virulence and invasiveness of S. Dublin in humans. Results We identified several virulence factors that form the bacterial invasome and may contribute to increasing bacterial virulence and pathogenicity including mainly Gifsy-2 prophage, two different type 6 secretion systems (T6SSs) harbored by Salmonella pathogenicity islands; SPI-6 and SPI-19 respectively and virulence genes; ggt and PagN. Although Vi antigen and the virulence plasmid have been reported previously to contribute to the virulence of S. Dublin we did not detect them in all invasive isolates indicating that they are not the main virulence determinants in S. Dublin. Conclusion Several virulence factors within the genome of S. Dublin might contribute to the ability of S. Dublin to invade humans’ blood but there were no genomic markers that differentiate invasive from non-invasive isolates suggesting that host immune response play a crucial role in the clinical outcome of S. Dublin infection

Efficient Physical Embedding of Topologically Complex Information Processing Networks in Brains and Computer Circuits

Nervous systems are information processing networks that evolved by natural selection, whereas very large scale integrated (VLSI) computer circuits have evolved by commercially driven technology development. Here we follow historic intuition that all physical information processing systems will share key organizational properties, such as modularity, that generally confer adaptivity of function. It has long been observed that modular VLSI circuits demonstrate an isometric scaling relationship between the number of processing elements and the number of connections, known as Rent's rule, which is related to the dimensionality of the circuit's interconnect topology and its logical capacity. We show that human brain structural networks, and the nervous system of the nematode C. elegans, also obey Rent's rule, and exhibit some degree of hierarchical modularity. We further show that the estimated Rent exponent of human brain networks, derived from MRI data, can explain the allometric scaling relations between gray and white matter volumes across a wide range of mammalian species, again suggesting that these principles of nervous system design are highly conserved. For each of these fractal modular networks, the dimensionality of the interconnect topology was greater than the 2 or 3 Euclidean dimensions of the space in which it was embedded. This relatively high complexity entailed extra cost in physical wiring: although all networks were economically or cost-efficiently wired they did not strictly minimize wiring costs. Artificial and biological information processing systems both may evolve to optimize a trade-off between physical cost and topological complexity, resulting in the emergence of homologous principles of economical, fractal and modular design across many different kinds of nervous and computational networks

Outbreak of Leishmania braziliensis cutaneous leishmaniasis, Saül, French Guiana [letter]

New World cutaneous leishmaniasis (CL), a zoonotic disease, is increasingly seen among travelers returning from Latin American countries, particularly from Bolivia, Belize, and French Guiana (1). The epidemiology of CL in the Americas is heterogeneous and has complex variations in transmission cycles, reservoir hosts, and sandfly vectors. Changing human activities that affect these factors may have resulted in the emergence of species with distinct pathogenic potentials and responses to therapy. In the Guianan ecoregion complex, leishmaniasis is endemic, and 5 coexisting Leishmania parasite species are known to infect humans: L. guyanensis, L. braziliensis, L. amazonensis, L. naiffi, and L. lainsoni. Among these species, L. guyanensis accounts for ≈85% of CL cases (2). We report an outbreak of 7 cases of L. braziliensis CL that occurred among 24 scientists who participated in a field mission at Limonade Creek in Saül, French Guiana, during October 10–25, 2013. Saül is an isolated village in the Amazonian rainforest (3°55′18′′N, 53°18′02′′W)