A study on the variability of Kappa (κ) in a borehole: Implications of the computation process

Knowledge of the acceleration spectral shape is crucial to various applications in engineering seismology. Spectral amplitude decays rapidly at high frequencies. Anderson and Hough (1984) introduced the empirical factor κ to model this attenuation. This is the first time κ is studied in a vertical array consisting of more than two stations. We use 180 earthquakes recorded at a downhole array with five stations in soils and rock to investigate the effect of soil conditions on κ. Given that κ computation processes vary across literature when following the classic Anderson–Hough method, we investigate its variability with the different assumptions that can be made when applying the method. The estimates of κ0 range between 0.017 and 0.031 s at the surface and between 0.004 and 0.024 s at rock. This variability due to the assumptions made is larger than the error of each estimate and larger than the average difference in values between sediment and rock. For this data set, part of it can be attributed to the type of distance used. Given this variability, κ0 values across literature may not always be comparable; this may bias the results of applications using κ0 as an input parameter, such as ground‐motion prediction equations. We suggest ways to render the process more homogeneous. We also find that κ at rock level is not well approximated by surface records from which we deconvolved the geotechnical transfer function. Finally, we compute κ on the vertical component and find a dependence of the vertical‐to‐horizontal κ ratio on site conditions

Un Cadavre qui donne des « signes de vie »

La venue au monde d’un enfant mort-né a toujours constitué pour le couple un profond traumatisme. Aux siècles passés où la destinée de l’âme était si importante dans le monde catholique, les parents recouraient volontiers à l’exposition du petit cadavre devant une Vierge miraculeuse dans l’espoir de lui voir donner les «  signes de vie  » qui autorisaient le baptême salvateur  : l’âme était sauvée et le cadavre pouvait alors être enterré en terre consacrée et non pas mis au rebut. Ce «  répit  » entre deux morts, puisque le corps de l’enfant redevenait cadavre après le miracle, se déroulait selon un rituel immuable. Dans le «  sanctuaire à répit  », pouvaient voisiner pendant des jours, voire des semaines, les dépouilles dénudées de plusieurs enfants exposés, dont les pèlerins surveillaient le comportement. Le retour de la chaleur et de la coloration du corps, les mouvements des membres, les épanchements aqueux et sanguins étaient interprétés comme des signes véritables de retour à la vie. À l’angoisse de la famille et de la communauté après la venue d’un enfant mort succédait l’enthousiasme des pèlerins. Le corps était ordinairement enterré dans le cimetière qui jouxtait le sanctuaire. Plus tard, les parents ne manqueraient pas de rendre hommage à la Vierge en offrant un ex-voto célébrant le miracle. Du xiv e au xiv e siècles, des milliers et des milliers de cadavres d’enfants mort-nés ont été ainsi exposés en France, Belgique, Suisse, Autriche, Allemagne du sud et Italie du nord. Si les praticiens (accoucheuses, chirurgiens et médecins) ont longtemps accepté de cautionner le miracle, ils commencent à prendre leurs distances à partir des années 1730-1740. Désormais, ce n’est plus le cadavre de l’enfant qui justifie leur intervention  ; ce qu’ils veulent c’est sauver l’enfant à sa naissance. L’Église de son côté a toujours été très divisée sur l’attitude à tenir à l’égard des enfants mort-nés voués au néant. Autant les curés faisaient volontiers preuve de tolérance voire de complicité à l’égard des «  répits  », autant la hiérarchie se montrait méfiante à l’égard de pratiques qu’elle jugeait entachées de magie et de tromperie. En fait, derrière la question du sacrement chrétien se devinent des comportements qui ont longtemps caractérisé le monde rural  : croyance à la «  chasse sauvage  » et volonté de restaurer par un rituel approprié l’équilibre un instant rompu de l’ordre du monde, puisque la naissance d’un enfant mort est toujours interprétée par la communauté comme le signe annonciateur de quelque calamité naturelle.The birth of a stillborn child has always been deeply traumatic for parents. In past centuries, when the Catholic Church regarded the destiny of the soul as highly important, parents would willingly expose the little corpse to the miraculous Virgin in the anticipation of signs of life which would allow for a saving baptism: its soul was saved et and the little corpse could then be buried in consecrated ground rather than being discarded. This ‘respite’ or period of limbo between two deaths was dealt with according to an immutable ritual.The remains of several children would remain in a respite sanctuary during days or even weeks, while pilgrims surveyed their behaviour. Any changes to the appearance of the body such as the release of bodily fluids or the perception of heat and colour were considered as signs of a return of life. The anguish of the family or the community after the birth of the stillborn child would then be replaced by the renewed enthusiasm of the religious community. The body was normally buried in the graveyard next to the sanctuary. Later on, the parents would ensure to pay tribute to the Virgin Mary by offering an ex-voto in celebraion of the miracle. From 14th to 19th century, many thousands of children corpses have been exposed in France, Belgium, Switzerland, Austria, southern Germany and northern Italy. Although medical practitioners (midwives, surgeons, doctors) remained sympathetic to the miracle for a long time, their position changed from around 1730-1740 onwards. Henceforth, saving the child at birth became the priority rather than simply post-mortem medical intervention.The Catholic Church, on the other hand, have always been ambiguous on what stance to adopt regarding the fate of the condemned souls of stillborn children. While parish priests could often show tolerance and even complicity towards ‘respite’ pratices, the ecclesiastical hierarchy were mistrustful and judged them as being tainted by occultism and delusion. Besides the importance of the Christian sacraments, these long lasting behaviours of rural society

High resolution quantitative seismic imaging of a strike-slip fault with small vertical o set in clay-rocks from underground galleries. Experimental Platform of Tournemire, France.

Imaging tectonic faults with small vertical offsets in argilittes (clay-rock) using geophysical methods is challenging. In the context of deep radioactive waste disposals, the presence of such faults has to be assessed since they can modify the rock confining properties. In the Tournemire Experimental Platform (TEP, France), fault zones with small vertical offsets and complex shape have been identified from underground works. However, 3D high-resolution surface seismic methods have shown limitations in this context that led us to consider the detection and characterization of the faults directly from underground works. We investigate here the potential of seismic full waveform inversion (FWI) applied in a transmission configuration to image the clay-rock medium in a horizontal plane between galleries, and compare it with first-arrival traveltime tomography (FATT). Our objective is to characterize seismic velocities of a block of argilittes crossed by a subvertical fault zone with a small vertical offset. The specific measurement configuration allows us to neglect the influence of the galleries on the wave propagation and to simplify the problem by considering a 2D isotropic horizontal imaging domain. Our FWI scheme relies on a robust adaptation of early-arrival waveform tomography. The results obtained with FATT and FWI are in accordance and both correlate with the geological observations from the gallery walls and boreholes. We show that even though various simplifications are done in the inversion scheme and only a part of the data is used, FWI allows to get higher resolution images than FATT, and is especially less sensitive to the incomplete illumination as it uses also diffracted energy. The results provided in this study highlight the complexity of the fault zone, showing a complex interaction of the main fault system with a secondary system composed of decimetric fractures associated with the presence of water

Free and smooth boundaries in 2-D finite-difference schemes for transient elastic waves

A method is proposed for accurately describing arbitrary-shaped free boundaries in single-grid finite-difference schemes for elastodynamics, in a time-domain velocity-stress framework. The basic idea is as follows: fictitious values of the solution are built in vacuum, and injected into the numerical integration scheme near boundaries. The most original feature of this method is the way in which these fictitious values are calculated. They are based on boundary conditions and compatibility conditions satisfied by the successive spatial derivatives of the solution, up to a given order that depends on the spatial accuracy of the integration scheme adopted. Since the work is mostly done during the preprocessing step, the extra computational cost is negligible. Stress-free conditions can be designed at any arbitrary order without any numerical instability, as numerically checked. Using 10 grid nodes per minimal S-wavelength with a propagation distance of 50 wavelengths yields highly accurate results. With 5 grid nodes per minimal S-wavelength, the solution is less accurate but still acceptable. A subcell resolution of the boundary inside the Cartesian meshing is obtained, and the spurious diffractions induced by staircase descriptions of boundaries are avoided. Contrary to what occurs with the vacuum method, the quality of the numerical solution obtained with this method is almost independent of the angle between the free boundary and the Cartesian meshing.Comment: accepted and to be published in Geophys. J. In

Expérience tablettes tactiles à l'école primaire - ExTaTE

86 pagesL' étude commanditée par le ministère de l'Éducation nationale français, a été menée en 2013-2014 par le laboratoire " École, Mutations et Apprentissages " (EMA) de l'université de Cergy-Pontoise. Elle porte sur l'utilisation des tablettes tactiles à l'école primaire. Deux enquêtes de terrain (observations filmées, entretiens, questionnaires) ont été menées à 6 mois d'intervalle en 2013-2014 auprès d'enseignants volontaires, leurs élèves et les personnels de supervision. Elles ont permis de documenter les conditions d'implantation, les éventuels changements dans les pratiques et la manière dont les tablettes enrichissent ou limitent l'activité d'apprentissage des élèves dans les situations observées. L'étude montre que l'école primaire se prête bien à la mise en œuvre en classe de ce type d'instrument en particulier au cours d'activités de production. Les enseignants attribuent à ces instruments des fonctions de production, de communication, d'entrainement, de consultation d'aides et de supervision de l'activité des élèves. Elle met à jour des cas d'usages à valeur ajoutée pour les élèves et montre que les utilisations des tablettes s'accomplissent souvent dans des systèmes d'instruments plus larges amenant à une complexification de l'ingénierie pédagogique. Des pratiques de supervision apparaissent, grâce à des applications permettant des allers et retours de documents, le contrôle en continu de la tâche et le réajustement des attentes de l'enseignant. Ces pratiques réclament une aisance instrumentale importante de l'enseignant et une vision claire de la perspective didactique qu'il poursuit et amènent les enseignants à réinterroger l'évaluation de l'activité des élèves : comment évaluer une tâche qui ne donne pas trace de son processus d'élaboration ou la collaboration entre élèves ou encore les compétences instrumentales qui se construisent ? Concernant l'activité des élèves producteurs d'écrits riches, les instruments permettent de réguler l'acte d'écriture dans le flux (correcteur orthographique, écriture prédictive). Les fonctions méta textuelles sont prometteuses, mais peu exploitées et des confusions du côté des élèves (cycle 2) apparaissent confrontant souvent les enseignants à des textes constitués des erreurs produites par les élèves et par la machine. 6 recommandations ferment le rapport. Elles concernent : - l'organisation nécessaire pour que les usages persistent : mise en réseau des équipes, valorisation, robustesse des infrastructures ; - l'accompagnement par les inspecteurs en charge des TICE et les animateurs TICE de leurs collègues dans la perspective d'équipements futurs : vision systémique des contraintes posées, approche didactique des ressources mobilisables, gestion de classe ; - compétences instrumentales des enseignants et développement de connaissances plus robustes en informatique ; - repenser une formation des enseignants à la gestion d'un système d'instruments orientée ingénierie éducative, incluant les aspects techniques, organisationnels pédagogiques, didactiques et ergonomiques ; - l'ouverture des applications, dans une dimension auteur, pour permettre une meilleure adaptation aux contextes locaux ; - accompagner les élèves à une meilleure compréhension du fonctionnement des environnements technologiques utilisés

Multidisciplinary Study of Seismic Wave Amplification in the Historical Center of Rome, Italy

Assessment of potential strong ground motion within the city of Rome is crucial to preserve its millenary monumental heritage and protect its large urban settlements. Rome is located at a distance of some tens of kilometers from the central Apennines seismogenic zone, where earthquakes of tectonic origin and of a magnitude of up to 7.0 are expected. The geological bedrock is mainly represented by high - consistency fine grained marine sedimentary deposits Pliocene to lower Pleistocene aged and named Monte Vaticano Unit. An upper Pleistocene – Holocene succession of fluvial deposits partially fill the paleo-valley of the Tiber river and of its tributaries formed during the last glacial period (22-18 kyr) carving the seismic bedrock. This alluvial body is composed by an heterogeneous fining-upward succession up to 60m thick. To better quantify the expected ground shaking within the city of Rome, a multidisciplinary research activity has being carried out and: i) a detailed 3D engineering-geology model of the Tiber River alluvia was obtained based on new data from the metro lines under construction; ii) 1D and 2D numerical modeling were performed; iii) effects due to the nonlinear behavior of soil have also been taken into account. The preliminary results show that the heterogeneity of the alluvial fill mainly controls the local seismic response. In addition, an interesting result is the fact that 1D amplification estimates are pervasively higher than the 2D ones

Multidisciplinary Study of Seismic Wave Amplification in the Historical Center of Rome, Italy

Assessment of potential strong ground motion within the city of Rome is crucial to preserve its millenary monumental heritage and protect its large urban settlements. Rome is located at a distance of some tens of kilometers from the central Apennines seismogenic zone, where earthquakes of tectonic origin and of a magnitude of up to 7.0 are expected. The geological bedrock is mainly represented by high - consistency fine grained marine sedimentary deposits Pliocene to lower Pleistocene aged and named Monte Vaticano Unit. An upper Pleistocene – Holocene succession of fluvial deposits partially fill the paleo-valley of the Tiber river and of its tributaries formed during the last glacial period (22-18 kyr) carving the seismic bedrock. This alluvial body is composed by an heterogeneous fining-upward succession up to 60m thick. To better quantify the expected ground shaking within the city of Rome, a multidisciplinary research activity has being carried out and: i) a detailed 3D engineering-geology model of the Tiber River alluvia was obtained based on new data from the metro lines under construction; ii) 1D and 2D numerical modeling were performed; iii) effects due to the nonlinear behavior of soil have also been taken into account. The preliminary results show that the heterogeneity of the alluvial fill mainly controls the local seismic response. In addition, an interesting result is the fact that 1D amplification estimates are pervasively higher than the 2D ones

Une méthode Galerkin discontinue d'ordre élevé pour la propagation d'ondes sismiques en milieu viscoélastique

We present a high-order discontinuous Galerkin method for the simulation of P-SV seismic wave propagation in heterogeneous media and two dimensions of space. The first-order velocity-stress system is obtained by assuming that the medium is linear, isotropic and viscoelastic, thus considering intrinsic attenuation. The associated stress-strain relation in the time domain being a convolution, which is numerically intractable, we consider the rheology of a generalized Maxwell body replacing the convolution by differential equations. This results in a velocity-stress system which contains additional equations for the anelastic functions including the strain history of the material. Our numerical method, suitable for complex triangular unstructured meshes, is based on a centered numerical flux and a leap-frog time-discretization. The extension to high order in space is realized by Lagrange polynomial functions, defined locally in each element. The inversion of a global mass matrix is avoided since an explicit scheme in time is used and because of the local nature of the discontinuous Galerkin formulation. The method is validated through numerical simulations including comparisons with a finite difference scheme.Nous présentons une méthode Galerkin discontinue d'ordre élévé pour la simulation de la propagation d'ondes sismiques P-SV en milieu hétérogène et en deux dimensions d'espace. Le système vitesse-contraintes du premier ordre est obtenu en supposant un milieu linéaire, isotrope et viscoélastique, prenant ainsi en compte l'atténuation intrinsèque du milieu. La relation contraintes-déformations dans le domaine temporel étant une convolution, qui nécessiterait une approximation numérique très coûteuse, nous considérons la rhéologie d'un "generalized Maxwell body" (GMB) remplaçant la convolution par un jeu d'équations différentielles. Il en résulte un système vitesse-contraintes contenant des équations supplémentaires pour les fonctions anélastiques qui traduisent l'historique de déformation du matériau. Notre méthode numérique, applicable à des maillages triangulaires non structurés, est basée sur des flux centrés et un schéma saute-mouton en temps. L'extension en espace à l'ordre élevé est obtenue grâce à des polynômes de Lagrange, définis localement dans chaque élément. La méthode étant explicite, elle ne nécessite pas d'inversion de matrice de masse globale. La méthode est validée via des simulations numériques, notamment des comparaisons avec un schéma aux différences finies

Simple Physical Approach to Thermal Cutting Rules

A first-principles derivation is given of the imaginary part of a Green's function in real-time thermal field theory. The analysis and its conclusions are simpler than in the usual circled-vertex formalism. The relationship to Cutkosky-like cutting rules is explained.Comment: 9 pages, plain tex, 5 figures embedded with epsf -- 2 typos correcte