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Piersanti, Antonio
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Piersanti, Antonio
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antonio.piersanti@ingv.it
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76 results
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- PublicationOpen AccessGrain size and flow volume effects on granular flow mobility in numerical simulations: 3-D discrete element modeling of flows of angular rock fragments.(2015)
; ; ;Cagnoli, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; 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.295 245 - PublicationOpen AccessApplication of the Post-Widder Laplace inversion algorithm to postseismic rebound models(2006-12-11)
; ; ; ; ;Cannelli, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Melini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Spada, G.; Institute of Physics, University of Urbino, Italy; ; ; The computation of global postseismic rebound in a spherically symmetric, stratified, self-gravitating Earth with Maxwell viscoelastic rheology can be carried out semi-analytically with a normal-mode approach. The solution scheme usually involves the application of standard propagator techniques to the equivalent problem in the Laplace domain; to recover the temporal dependence a numerical Laplace anti-transform is required. This step involves the solution of the so-called “secular equation”, whose degree increases linearly with the detail of the stratification modeling, and whose coefficients become extremely ill-conditioned for high harmonic orders. As a result, the practically solvable models are limited to a few viscoelastic layers, and are anyway affected by severe numerical instabilities. To overcome these difficulties, alternative approaches have been explored by several authors, ranging from Runge-Kutta purely numerical integration to the evaluation of Laplace antitransform by a numerical discretization of the Bromwich integral. The Post-Widder algorithm allows the estimation of the Laplace antitransform by sampling numerically the transform on the positive real axis. This method, which has been recently applied to the computation of GIA viscoelastic Love numbers, allows to bypass completely the root-finding procedure while preserving at the same time the analytical normal-mode solution form. In this work, we apply the Post-Widder method to the computation of post-seismic rebound models. We perform a series of benchmarks to optimize the algorithm for speed while checking its stability against earlier results.180 381 - PublicationOpen AccessGlobal seismic tomography and modern parallel computers(2006-06-05)
; ; ; ;Soldati, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Boschi, L.; E.T.H. Z¨urich, Switzerland ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; A fast technological progress is providing seismic tomographers with computers of rapidly increasing speed and RAM, that are not always properly taken advantage of. Large computers with both shared-memory and distributedmemory architectures have made it possible to approach the tomographic inverse problem more accurately. For example, resolution can be quantified from the resolution matrix rather than checkerboard tests; the covariance matrix can be calculated to evaluate the propagation of errors from data to model parameters; the L-curve method can be applied to determine a range of acceptable regularization schemes. We show how these exercises can be implemented efficiently on different hardware architectures.392 1249 - PublicationOpen AccessSignature of asthenospheric viscosity on long wavelength postseismic gravity perturbations after the 2004 Sumatra earthquake(2007-04)
; ; ; ;Cannelli, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Melini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; Using a theoretical model of global postseismic deformation we computed the effect of 2004 Sumatra earthquake on the time evolution of the low degree zonal coefficients of the Earth gravity field (Jn). In fact, it is reasonable to expect that the exceptional energy release of the Sumatra event has given rise to a perturbation of the long wavelength Earth’s gravity field due to internal mass redistribution. Our analysis is performed varying asthenosphere viscosities, in order to show how the expected signature of the seismic event on the long wavelength deformation field is sensitive to mantle rheology. Low asthenospheric viscosities yield very large Jn variation rates in the first years after the event. Our results show that on the J2 time-series the postseismic effect remains comparable with the main secular trend for several years after the event if an asthenospheric viscosity of 10^18 Pa s is assumed, while for lower values the signature in the data should be even stronger. Since these short time-scale effects are not easily discernible from the available geodetic data because of large seasonal signals, we computed the expected contribution of postseismic relaxation to long term Jn trends as a function of asthenospheric viscosity. Our results show that the viscoelastic relaxation leaves a not negligible signature on the long term measured time-histories. In the forthcoming years, when geodetic data from recent missions (such as GRACE) will be available, it will be possible to establish if, after the Sumatra event, a significant deviation of Jn time series from its secular trend occurred. In this case it should be possible to infer or at least to put constrains to the mean asthenospheric viscosity that is still one of the big open issues in mantle rheology.152 222 - PublicationOpen AccessPostseismic relaxation of the 2007 Central Peru earthquake(2007-12-10)
; ; ; ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cannelli, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Melini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; We present a comprehensive modeling of coseismic and postseismic effects of the 2007 Central Peru earthquake on deformation, gravity and stress fields obtained with a semi-analytical spherical self-gravitating Earth model. We discuss the expected signature of different stratification profiles including Maxwell and Burgers rheologies and find that measurements of short-term relaxation on horizontal deformations should provide a discrimination between different rheologies. We compute the time-dependent stress transfer of the 2007 earthquake on the 1868 and 1877 seismic gaps in terms of the Coulomb Failure Function (CFF). We find significant levels of stress transfer only on the 1868 seismic gap due to its proximity to the 2007 source, even if the sign of CFF variation is dependent on the depth of the receiver plane, which is not univocally fixed by geological evidences.133 96 - PublicationOpen AccessSmart working e Ricerca: il punto di vista dei Ricercatori e Tecnologi dell’INGV(2021-05-19)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Obiettivi: Le finalità di questo articolo sono quelle di sottolineare le specificità della Ricerca rispetto alla amministrazione. Metodologia: è stata svolta un’analisi qualitativa giuridico-normativa e una indagine online quantitativa a 585 ricercatori e tecnologi dell’INGV sullo smart working. Risultati: nell’articolo vengono richiamate le norme che affermano come le attività di ricerca e le attività gestionali debbono avere una valutazione diversa. Inoltre, il CCNL della sezione Ricercatori e Tecnologi già rende “smart” e “agile” il lavoro di ricerca senza ricadere nella legge sullo smart working. Le risposte all’indagine mostrano una forte coesione nel rivendicare i principi di autonomia e libertà della ricerca. Limiti e implicazioni: negli EPR si fa Ricerca e la Ricerca ha bisogno di flessibilità e specificità organizzativa rispetto ad una P.A. prevalentemente amministrativa e lo smart working mal si adatta al mondo della Ricerca. Originalità: il percorso bottom-up di rivendicazione dei diritti della ricerca, attraverso interviste online, è originale e innovativo per evidenziare l’analisi delle criticità del lavoro agile che non deve essere applicato senza considerare il modello rispondente alle proprie esigenze e caratteristiche.768 88 - PublicationRestrictedCUBIT and seismic wave propagation based upon the Spectral-Element Method: An advanced unstructured mesher for complex 3D geological media(2008)
; ; ; ; ; ; ;Casarotti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Stupazzini, M.; Department of Earth- and Environmental Sciences, Ludwig-Maximilians-Universitat, Munich, Germany ;Lee, S. J.; Institute of Earth Science, Academia Sinica. Taipei, Taiwan ;Komatitsch, D.; Laboratoire de Modlisation et d’Imagerie en Gosciences UMR 5212, Universit de Pau et des Pays de l’Adour., Pau, France ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Tromp, J.; Seismological Laboratory, California Institute of Technology, Pasadena, California, USA; ; ; ; ; ; ; ; ;Brewer, M. L.Marcum, D.Unstructured hexahedral mesh generation is a critical part of the model- ing process in the Spectral-Element Method (SEM). We present some ex- amples of seismic wave propagation in complex geological models, automati- cally meshed on a parallel machine based upon CUBIT (Sandia Laboratory, cubit.sandia.gov), an advanced 3D unstructured hexahedral mesh genera- tor that offers new opportunities for seismologist to design, assess, and improve the quality of a mesh in terms of both geometrical and numerical accuracy. The main goal is to provide useful tools for understanding seismic phenomena due to surface topography and subsurface structures such as low wave-speed sedimentary basins. Our examples cover several typical geophysical problems: 1) “layer-cake” volumes with high-resolution topography and complex solid- solid interfaces (such as the Campi Flegrei Caldera Area in Italy), and 2) models with an embedded sedimentary basin (such as the Taipei basin in Taiwan or the Grenoble Valley in France).236 31 - PublicationOpen AccessFEMSA: a finite element simulation tool for quasi-static seismic deformation modeling(2007-06)
; ; ; ;Volpe, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Melini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; 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 for details), and is freely distributed by request.2579 73508 - PublicationOpen AccessGeomorphologic observations and physical hypothesis on Martian gulliesWe propose a hypothesis to explain the erosive phenomenon of Martian gullies under current climatic conditions. This model is consistent with the morphology and finds support in the characteristic geographic diffusion of the gullies, which seem to avoid exposure to the sun and the hottest latitudes. We hypothesize a transient flow of spring water fed by melting permafrost which can occur only in certain latitudes and altitudes, with seasonal variability and for a very short time. Furthermore, this phenomenon can only occur in certain ranges of temperature and pressure, therefore when particular and sporadic weather conditions allow it. For this reason, we propose to call it weather-springing water (WSW).
184 89 - PublicationOpen AccessImpact of Sumatra earthquake on CMB topography and core ellipticity(2006-11)
; ; ; ;Cannelli, Valentina; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Melini, Daniele; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Piersanti, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; Characterization of the global impact of 2004 Sumatra earthquake event through the investigation of its effects on core-mantle boundary (CMB) shape and on the elliptical part of the gravity field (J2)153 108