771 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

    Grain size and flow volume effects on granular flow mobility in numerical simulations: 3-D discrete element modeling of flows of angular rock fragments.

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    The results of three-dimensional discrete element modeling (DEM) presented in this paper confirm the grain size and flow volume effects on granular flow mobility that were observed in laboratory experiments where batches of granular material traveled down a curved chute. Our numerical simulations are able to predict the correct relative mobility of the granular flows because they take into account particle interactions and, thus, the energy dissipated by the flows. The results illustrated here are obtained without prior fine tuning of the parameter values to get the desired output. The grain size and flow volume effects can be expressed by a linear relationship between scaling parameters where the finer the grain size or the smaller the flow volume, the more mobile the centre of mass of the granular flows. The numerical simulations reveal also the effect of the initial compaction of the granular masses before release. The larger the initial compaction, the more mobile the centre of mass of the granular flows. Both grain size effect and compaction effect are explained by different particle agitations per unit of flow mass that cause different energy dissipations per unit of travel distance. The volume effect is explained by the backward accretion of the deposits that occurs wherever there is a change of slope (either gradual or abrupt). Our results are relevant for the understanding of the travel and deposition mechanisms of geophysical flows such as rock avalanches and pyroclastic flows

    Core-mantle boundary deformations and J2 variations resulting from the 2004 Sumatra earthquake

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    The deformation at the core-mantle boundary produced by the 2004 Sumatra earthquake is investigated by means of a semi-analytic theoretical model of global coseismic and postseismic deformation, predicting a millimetric coseismic perturbation over a large portion of the core-mantle boundary. Spectral features of such deformations are analysed and discussed. The time-dependent postseismic evolution of the elliptical part of the gravity field (J2) is also computed for different asthenosphere viscosity models. Our results show that, for asthenospheric viscosities smaller than 10^18 Pa s, the postseismic J2 variation in the next years is expected to leave a detectable signal in geodetic observations.Comment: 14 pages, 8 figures, 1 table. It will appear in Geophysical Journal Internationa

    On the mass of supernova progenitors: the role of the 12^{12}C+12+^{12}C reaction

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    A precise knowledge of the masses of supernova progenitors is essential to answer various questions of modern astrophysics, such as those related to the dynamical and chemical evolution of Galaxies. In this paper we revise the upper bound for the mass of the progenitors of CO white dwarfs (\mup) and the lower bound for the mass of the progenitors of normal type II supernovae (\mups). In particular, we present new stellar models with mass between 7 and 10 \msun, discussing their final destiny and the impact of recent improvements in our understanding of the low energy rate of the \c12c12 reaction.Comment: To be published on the proceedings of NIC 201

    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‚ÄďAndaman 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

    The Influence of N14(e-,nu)C14(alpha,gamma)O18 reaction on the He-Ignition in Degenerate Physical Conditions

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    The importance of NCO chain on the onset of the He-flash in degenerate physical conditions has been reevaluated. We find that low-mass, metal-rich (Z ‚Č•\ge 0.001) structures climbing the Red Giant Branch do never attain the physical conditions suitable for the onset of this chain, while at lower metallicities the energy contribution provided by NCO reaction is too low to affect the onset of the central He-flash. At the same time, our evolutionary models suggest that for a Carbon-Oxygen White Dwarf of mass M_{WD}=0.6 M_sun accreting He-rich matter, directly or as a by-product of an overlying H-burning shell, at rates suitable for a dynamical He-flash, the NCO energy contribution is not able to keep hot enough the He-shell and in turn to avoid the occurrence of a strong electron degeneracy and the ensuing final explosion.Comment: 15 pages, 3 tables, 10 figure, to appear in Ap

    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
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