Volcanic deformation and flank instability due to magmatic sources and frictional rheology: the case of Mount Etna

The overall picture of Mount Etna deformation emerging since a couple of decades of geodetic surveys shows effects of magma accumulation, characterized by inflation/deflation cycle, accompanied by a sliding instability of the southeast flank, whose manifestation is an increase in the horizontal deformation away from the volcano summit. This is a very interesting case to test whether advanced models, taking into account topography, internal structure and frictional rheology, may contribute to a better understanding of the complex interplay among mechanical response, magmatic activity and gravitational load occurring in a volcanic system. Using finite element numerical models we make predictions of surface displacements associated with a simple expansion source and with a dike like vertical discontinuity. A new methodology is developed to initalize the lithostatic stress field according to the material and geometrical complexities of the models considered. Our results show that, while an amplification of the horizontal displacement can be easily obtained up to a maximum distance of 10 km from the source, we have not been able to find any onfiguration to extend further this signal. For the case of Mount Etna this suggests that the large horizontal displacements observed in the east flank along the coast cannot be directly related to magma accumulation below the volcano's summit

Analytical and 3-D numerical modelling of Mt. Etna (Italy) volcano inflation

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The psychometric properties of the CFSS-DS for schoolchildren in Saudi Arabia:a confirmatory factor analytic approach

Aim to test the psychometric properties of an Arabic version of the Child Fear Survey Schedule‐Dental Subscale (CFSS‐DS) a using confirmatory factor analysis. Methods 2 convenience samples were obtained: Sample [1]: 600 boys (33%) and girls attending 4 public schools in Onizah and Sample [2] 800 girls attending 8 public schools in Buridah. The questionnaire asked the participant's age, gender and completion of the CFSS‐DS. The data were subjected to exploratory factor analysis (EFA), parallel factor analysis, Cronbach alpha, confirmatory factor analysis (CFA) and goodness of fit statistics. Results 513 children in Sample [1] and 503 children in Sample [2] participated giving a valid response rate of 86% and 67% respectively. From the EFA 3 factors were identified and confirmed statistically using parallel factor analysis. The internal consistency of the 3‐factors, dental fear subscale (0.86); hospital fear subscale (0.77) and stranger fear subscale (0.71) was good. The CFA showed that the current EFA model was an equivalent fit to the El Housseiny et al1 model, however, the solution using El Housseiny et al's structure was distorted. Conclusions A 3‐factor structure with acceptable reliability exists for this Arabic version of the CFSS‐DS, confirmed by a CFA using an additional data set.PostprintPeer reviewe

Ottimizzazione del processo di riscaldo per tempra di grandi fucinati mediante analisi FEM

In questo lavoro è presentata la simulazione del processo di riscaldo per austenitizzazione di grandi fucinatiin acciaio destinati alla tempra differenziale. In ogni trattamento termico, le grandezze controllabili a livelloindustriale sono il tempo e la temperatura. È quindi agendo su queste che si può ottimizzare il processo perottenere le proprietà e le microstrutture desiderate per l’acciaio esaminato, e in definitiva massimizzare laqualità del pezzo finale. I prodotti analizzati sono i cilindri di laminazione fucinati, la cui produzione richiede unattento ciclo termico successivo alla deformazione plastica. Infatti, dopo un ciclo termico preliminare di ricotturacon lo scopo di facilitare le lavorazioni di sgrossatura alle macchine utensili, questi pezzi vengono sottopostiad una tempra differenziale per incrementare la durezza dello strato di lavoro, il cui spessore varia in funzionedelle specifiche richieste dal cliente. L’ottimizzazione di un processo può essere implementata utilizzando leggiempiriche ed il proprio know-how in prove sperimentali. La simulazione numerica rappresenta uno strumentodi previsione che potrebbe favorire un approccio più sistematico e scientifico alla risoluzione, in fase diprogetto, di tali problematiche industriali, specialmente quando il rapporto di scala tra il provino sperimentaleed il componente reale è molto elevato, come nel caso oggetto del presente lavoro. Lo strumento numericotipicamente adottato per simulare tale processo è la modellazione e l’analisi agli elementi finiti (FEM). Avendocome possibili parametri il livello di suddivisione del modello (meshatura), le caratteristiche chimico-fisiche delmateriale ed i parametri di scambio termico (entrambe differenziabili topologicamente all’interno del modellostesso) l’approccio FEA consente di simulare sia la forgiatura che i trattamenti termici ed in particolare le fasi diriscaldo, mantenimento e raffreddamento. I risultati ottenibili sono il campo termico, la distribuzione delle variefasi ed i valori di tensioni residue derivanti dal trattamento termico stesso. I risultati sono monitorabili nell’interoarco temporale del processo. Questo tipo di analisi agli elementi finiti consente di prevedere le proprietà delpezzo nell’intero arco temporale del processo: una volta caratterizzato il materiale ed i forni di riscaldo, si haa disposizione uno strumento capace di prevedere in maniera affidabile i risultati di un trattamento termico. Ilsoftware utilizzato in questo studio è il codice FEM commerciale Forge

Analisi del processo di deformazione a caldo e dell’evoluzione microstrutturale di un acciaio al 3% Cr mediante prove di torsione

Lo studio dell’evoluzione della microstruttura durante il processo di deformazione plastica di acciai rivestefondamentale importanza. In questo lavoro è stato analizzato il comportamento a deformazione a caldo di unacciaio 3% Cr tramite prove di torsione eseguite nell’intervallo di temperatura 1000?1200°C e con e.compresatra 0.01 e 1.00s-1. L’analisi condotta ha consentito di determinare le costanti della legge di potenza che regolail processo di deformazione a caldo (A0 , Q ed n ) tramite le quali è possibile ottimizzare i processi industriali.L’evoluzione microstrutturale durante la deformazione a caldo è stata valutata in termini di grado di percentualedi fase ricristallizzata ed è analizzata attraverso microscopia elettronica a trasmissione (TEM) e microscopiaad orientazione di immagine-diffrazione da retrodiffusione elettronica (OIM?EBSD). In particolare attraversoquesta ultima tecnica viene stimata la frazione volumetrica di ricristallizzato in termini di parametro GOS (GrainOrientation Spread), che meglio sembra interpretare l’evoluzione microstrutturale dopo deformazione a caldo inmicrostrutture martensitiche

Stress, strain and mass changes at Mt. Etna during the period between the 1991–93 and 2001 flank eruptions

During the ~8-year period between the 1991–93 and 2001 flank eruptions, the eruptive activity of Mt. Etna was confined to the summit craters. Deformation and tomography studies indicate that this activity was fed by a magma accumulation zone centered NE of the summit, at a depth of 5 to 9 km below sea level. The most significant gravity changes measured during the same period were induced by mass redistributions at shallower depth below the southeastern flank of the volcano, where minor ground deformation was observed (i.e., vertical displacements within 2 cm). The mismatch between the position of pressure and mass sources is difficult to explain under the assumption that both are directly related to magma dynamics. Past studies have suggested that the gravity changes observed during 1994–2001 may primarily reflect changes in the rate of microfracturing along the NNW–SSE fracture/weakness zone (FWZ) that crosses the SE slope of Etna. We use the finite element method to shed new light on the complex relations between stress, strain and mass changes that occurred at Etna during the studied period. In particular, following previous results on the degradation of the mechanical properties of rocks, we perform a set of simulations assuming that the part of the medium containing the FWZ is characterized by a lower Young's modulus than would be expected from interpolation of tomographic data. We find that the presence of the FWZ creates a distortion of the displacement field induced by the deeper pressure source, locally resulting in a weak extensional regime. This finding supports the hypothesis of a cause–effect relationship between pressurization beneath the NW flank and tensile extension beneath the SE slope of the volcano. We propose that this extensional regime enhanced the propagation of pressurized gas, that, in turn, amplified the tensile strain across the FWZ. We also find that decreasing the value of Young's modulus in the FWZ allows for a larger amount of extension at depth, with no change in the magnitude of surface displacements. This result provides an indication of how the changes in the rate of microfracturing at depth, which are needed to induce the observed gravity changes, might have occurred without large ground deformation

3D Finite element modeling of stress interaction: an application to Landers and Hector Mine fault systems

We model the coseismic and postseismic stress changes and the surface deformation caused by earthquake dislocations through a three-dimensional (3-D) finite element numerical procedure applied to the 1992 Landers and the 1999 Hector Mine earthquakes. Our goal is to investigate the stress interaction between these complex nonplanar fault systems. The modeling strategy proposed in this study allows the calculation of elastic deformation and Coulomb stress changes either by imposing the slip distribution as a boundary condition along assigned faults or by retrieving the slip pattern on preexisting faults imposing the regional stress field. We study how different initial stress conditions ( including the depth dependence of isotropic components of the regional stress), different values of Coulomb friction coefficient, and the 1-D rigidity layering can affect the slip pattern on assumed faults and the resulting Coulomb stress changes. We propose here an original approach to simultaneously model slip distribution, surface deformation, and stress perturbations consistently with the rheological parameters of the lithosphere and its state of stress.PublishedB05S173.1. Fisica dei terremotiJCR Journalrestricte

Isostatic rebound following the Alpine deglaciation: impact on the sealevel variations and vertical movements in the Mediterranean region

The present-day sea level variations and geodetically observed ground deformations in the Mediterranean area are normally ascribed to the combined effect of tectonic or human-driven subsidence and postglacial uplift as a result of the melting of the major Pleistocene ice sheets. However, another potential cause of deformation, only marginally considered to date, is the melting of the glacier that covered the Alps during the last glacial maximum (LGM). The aim of this paper is to predict the long-term sea level variations induced by the melting of both the late-Pleistocene and Alpine ice sheets and compare our results with the relative sea level (RSL) observations available in the Mediterranean region. This task is accomplished solving the sea level equation (SLE) for a spherically symmetric viscoelastic Earth. Our analysis shows that the melting of the Alpine glacier has marginally affected the Holocene sea level variations in the near-field sites in southern France (Marseilles and Roussillon) and the central Tyrrhenian sea (Civitavecchia), and that the RSL predictions are significantly sensitive to the chronology of the remote ice aggregates. The computations, which are performed using a specific mantle viscosity profile consistent with global observations of RSL rise, show that the uplift rate driven by the Alpine isostatic readjustment may account for up to 1/3 of the rates observed at GPS stations in the western portion of the chain. Our results suggest that a thorough modelization of both near- and far-field ice sheets is necessary to gain a better insight into the present-day deformations and sea level variations in the Mediterranean region

Isostatic rebound following the Alpine deglaciation: impact on sealevel variations and vertical movements in the Mediterranean region

none3noThe present-day sea level variations and geodetically observed ground deformations in the Mediterranean area are normally ascribed to the combined effect of tectonic or human-driven subsidence and postglacial uplift as a result of the melting of the major Pleistocene ice sheets. However, another potential cause of deformation, only marginally considered to date, is the melting of the glacier that covered the Alps during the last glacial maximum (LGM). The aim of this paper is to predict the long-term sea level variations induced by the melting of both the late-Pleistocene and Alpine ice sheets and compare our results with the relative sea level (RSL) observations available in the Mediterranean region. This task is accomplished solving the sea level equation (SLE) for a spherically symmetric viscoelastic Earth. Our analysis shows that the melting of the Alpine glacier has marginally affected the Holocene sea level variations in the near-field sites in southern France (Marseilles and Roussillon) and the central Tyrrhenian sea (Civitavecchia), and that the RSL predictions are significantly sensitive to the chronology of the remote ice aggregates. The computations, which are performed using a specific mantle viscosity profile consistent with global observations of RSL rise, show that the uplift rate driven by the Alpine isostatic readjustment may account for up to 1/3 or the rates observed at GPS stations in the western portion of the chain. Our results suggest that a thorough modelization of both near- and far-field ice sheets is necessary to gain a better insight into the present-day deformations and sea level variations in the Mediterranean region.N/ArestrictedP. STOCCHI; SPADA G.; S. CIANETTIP., Stocchi; Spada, Giorgio; S., Cianett