1,946 research outputs found

    Impact of global seismicity on sea level change assessment

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    We analyze the effect of seismic activity on sealevel variations, by computing the time-dependent vertical crustal movement and geoid change due to coseismic deformations and postseismic relaxation effects. Seismic activity can affect both the absolute sealevel, by changing the Earth gravity field and hence the geoid height, and the relative sealevel, i.e. the radial distance between seafloor and geoid level. By using comprehensive seismic catalogues we assess the net effect of seismicity on tidal relative sealevel measurements as well as on the global oceanic surfaces, and we obtain an estimate of absolute sealevel variations of seismic origin. Our results confirm that, on a global scale, most of the signal is associated with few giant thrust events, and that RSL estimates obtained using tide-gauge data can be sensibly affected by the seismic driven sealevel signal. The recent measures of sealevel obtained by satellite altimetry show a wide regional variation of sealevel trends over the oceanic surfaces, with the largest deviations from the mean trend occurring in tectonically active regions. While our estimates of average absolute sealevel variations turn out to be orders of magnitude smaller than the satellite measured variations, we can still argue that mass redistribution associated with aseismic tectonic processes may contribute to the observed regional variability of sealevel variations.Comment: 34 pages, submitted to Journal of Geophysical Researc

    HPC in global geodynamics: Advances in normal-mode analytical modeling

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    Analytical models based on normal-mode theory have been successfully employed for decades in the modeling of global response of the Earth to seismic dislocations, postglacial rebound and wave propagation. Despite their limited capabilities with respect to fully numerical approaches, they are yet a valuable modeling tool, for instance in benchmarking applications or when automated procedures have to be implemented, as in massive inversion problems when a large number of forward models have to be solved. The availability of high-performance computer systems ignited new applications for analytical modeling, allowing to remove limiting approximations and to carry out extensive simulations on large global datasets

    Extracting the top-quark running mass using ttt\bar{t}+1-jet events produced at the Large Hadron Collider

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    We present the calculation of the next-to-leading order QCD corrections for top-quark pair production in association with an additional jet at hadron colliders, using the modified minimal subtraction scheme to renormalize the top-quark mass. The results are compared to measurements at the Large Hadron Collider run I. In particular, we determine the top-quark running mass from a fit of the theoretical results presented here to the LHC data

    On the earthquake predictability of fault interaction models

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    Space-time clustering is the most striking departure of large earthquakes occurrence process from randomness. These clusters are usually described ex-post by a physics-based model in which earthquakes are triggered by Coulomb stress changes induced by other surrounding earthquakes. Notwithstanding the popularity of this kind of modeling, its ex-ante skill in terms of earthquake predictability gain is still unknown. Here we show that even in synthetic systems that are rooted on the physics of fault interaction using the Coulomb stress changes, such a kind of modeling often does not increase significantly earthquake predictability. Earthquake predictability of a fault may increase only when the Coulomb stress change induced by a nearby earthquake is much larger than the stress changes caused by earthquakes on other faults and by the intrinsic variability of the earthquake occurrence process

    New insights on the Messina 1908 seismic source from post-seismic sea level change

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    The identification of a source model for the catastrophic 1908 December 28 Messina earth- quake (Mw = 7.2) has been the subject of many papers in the last decades. Several authors proposed different models on the basis of seismological, macroseismic and geodetic data sets; among these models, remarkable differences exist with regard to almost all parameters. We selected a subset of six models among those most cited in literature and used them to model the post-seismic sea level variation recorded at the tide gauge station of Messina (until 1923), to attempt an independent discrimination among them. For each model, we assumed a simple rheological structure and carried out a direct-search inversion of upper crust thickness and lower crust viscosity to fit the post-seismic sea level signal. This approach enabled us to iden- tify a class of fault geometries which is consistent with the post-seismic signal at the Messina tide gauge and with the known structural and rheological features of the Messina strai

    A Sea Level Equation for seismic perturbations

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    Large earthquakes are a potentially important source of relative sea level variations, since they can drive global deformation and simultaneously perturb the gravity field of the Earth. For the first time, we formalize a gravitationally self-consistent, integral sea level equation suitable for earthquakes, in which we account both for direct effects by the seismic dislocation and for the feedback from water loading associated with sea level changes. Our approach builds upon the well-established theory first proposed in the realm of glacio-isostatic adjustment modelling. The seismic sea level equation is numerically implemented to model sea level signals following the 2004 Sumatra鈥揂ndaman earthquake, showing that surface loading from ocean water redistribution (so far ignored in post-seismic deformation modelling) may account for a significant fraction of the total computed post-seismic sea level variatio

    Trade--Off Between Seismic Source Detail and Crustal Heterogeneities in Spherical 3D Finite Element Modeling: the 2004 Sumatra Earthquake case-study

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    Finite Element methods (FEMs) are a powerful numerical simulation tool for modeling seismic events as they allow to solve three-dimensional complex models. We used a 3D Finite Element approach to evaluate the co-seismic displacement eld produced by the devastating 2004 Sumatra Andaman earthquake, which caused permanent deformations recorded by continuously operating GPS networks in a region of unprecedented extent. Previous analysis of the static displacement fi eld focused on the heterogeneous distribution of moment release on the fault plane; our intention here is to investigate how much the presence of crustal heterogeneities trades off seismic source details. To this aim, we adopted a quite simple source model in modeling the event. The key feature of our analysis is the generation of a complex three dimensional spherical domain. More-over, we also made an accurate analysis concerning boundary conditions, which are crucial for FE simulations

    Hemangioendotelioma epitelioide solitario de hueso: Aportaci贸n de dos nuevos casos

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    El hemangioendotelioma epitelioide, caracterizado por c茅lulas endoteilales epitelioides o "histiocitoides", en su variantes 贸sea solitaria, es una neoplasia de dif铆cil diagn贸stico, pron贸stico incierto y evoluci贸n impredecible. De etiolog铆a poco clara e infrecuente en su localizaci贸n 贸sea, sigue un curso cl铆nico muy variable. La multicentricidad y la multifocalidad son dos caracter铆sticas fundamentales de esta neoplasia, con predilecci贸n por las extremidades inferiores por ello, las lesiones solitarias pueden ser dif铆ciles de diagnosticar confundi茅ndose con carcinomas metast谩ticos y otras entidades. Su tratamiento no est谩 claramente establecido y su potencial de agresividad es impredecible, hasta tal punto que la cirug铆a ablativo puede ser m谩s frecuente de lo hsta ahora publicado. Su diagn贸stico y tratamiento deben ser exhaustivos ya que se han descrito comportamientos agresivos en tumores de bajo grado de malignidad con evoluciones insidiosas que terminan en recidivas tumorales. Los tres pilares en que se debe basar el tratamiento son: la resecci贸n en bloque, cobertura completa del defecto 贸seo y radioterapia postoperativa.Solitary epithelioid hemangioendothelioma of bone, characterized by epitheliolid or "histiocytoid" endotelial cells has a difficult diagnosis, confusing or unknown prognosis and unpredictable outcome. Infrequently recognized in bone, its etiology is not clear with a very variable clinical course. Multicentricity andmultifocality are two characteristics of this tumour, with a predilection for lower extremity bones. Therefore solitary lesions may be difficult to diagnose being confused with metastatic carcinomas and other entities. Its treatment is not well established. Their aggressive potential is unpredictable, to such a point that ablative surgery may be more frequent than previous reports have shown. Its diagnosis and treatment must be exhaustive as aggressive behaviour with insidious evolutions ending as relapses have been described the three pillar on which we will base its treatment are: in-block resection, complete coverage of the residual bone lesion and postoperative radiotherapy

    FEMSA: a finite element simulation tool for quasi-static seismic deformation modeling

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    We set up a computational tool to numerically model static and quasi-static deformation generated by faulting sources embedded in plane or spherical domains. We use a Finite Element (FE) approach to automatically implement arbitrary faulting sources and calculate displacement and stress fields induced by slip on the fault. The package makes use of the capabilities of CalculiX, a non commercial FE software designed to solve field problems (see <http://www.calculix.de> for details), and is freely distributed by request

    Finite Element Modeling of the 2004 giant Sumatra Earthquake Postseismic Displacement Field

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    The 26 December 2004 Sumatra-Andaman earthquake is one of the largest earthquakes ever recorded since 1900. The earthquake resulted from complex slip on the fault where the oceanic portion of the Indian Plate slides under the Eurasian Plate, by the Indonesian Island of Sumatra. The particular features of the detected quasi-static displacement field has been previously attributed to the heterogeneous distribution of moment release on the fault plane. In the present work, we use a new computational FEM strategy to model the co- and postseismic displacement field associated with the Sumatra earthquake. For the first time we can study the joint effects of sphericity and 3D mechanical and rheological heterogeneities on the investigated observables. The comparison between our synthetic results and the available deformation data allows us to ascertain if also lateral heterogeneities in the physical properties of the medium could have played a role in assessing the deformation field
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