1,721,001 research outputs found
TO SEEP OR NOT TO SEEP? SOME CONSIDERATIONS REGARDING WATER INFILTRATION IN VOLCANIC LAKES
No full textRainfall Induced Horizontal Deformation in the European Eastern Alps Measured by GPS
No full textWe analyzed the time-series of continuous GPS stations operating in the Italian, Austrian, Slovenian and Croatian Alps and Dinarides with a blind-source-separation algorithm based on a variational Bayesian Independent Component Analysis method, characterizing the spatiotemporal evolution of ground displacements and crustal deformation associated to hydrological processes over a vast area of ~70.000 km2. The study area is part of the broad zone of deformation where the N-S Adria-Eurasia convergence and the E-ward escape of the Eastern Alps toward the Pannonian basin are accommodated. We characterized the spatial response and the temporal evolution of several signals, among which the most significant ones are two annual signals with spatially uniform response in the vertical and horizontal components, respectively, and a time-variable, non-cyclic, signal characterized by a spatially variable response in the horizontal components. Because of its non-uniform spatial response, this latter signal induces a succession of extensional/compressional deformation, which is larger in areas characterized by karst geology, varying in amplitudes during the study time-span (2007-2016). The orientation of the principal time-variable strain-axes is normal to the orientation of lineaments and fractures detected from the analysis of a digital elevation model and parallel to the direction of tectonic stress. We have compared the time evolution of this signal with hydrological observations by exploiting the availability of gridded datasets for the European area. The detected deformation signal is highly correlated with cumulated rainfall over a period of 180 days, suggesting that the opening of fractures in karst rocks caused by cumulated rainfall is likely the primary mechanism of this deformation signal, whose kinematics is guided by the orientation of rock's fractures. We discuss the implication that this time-variable non-tectonic deformation may have for the estimate of the long-term interseismic strain accumulation and the seismic potential of active faults in the study area
Modellare l'interazione tra terremoti e fluidi: effetti superficiali sulla circolazione dei fluidi del sottosuolo e sismicità indotta nell'attività geotermica profonda.
Full text linkThe interaction between earthquakes and crustal fluids is a very complex topic due to several mechanisms that are involved and which influence each other.
Some phenomena, like the alterations of springs discharge rates and fluid flow, liquefaction and changing of the water levels in phreatic wells are largely documented in the literature, but their explanation is not yet fully clear. Furthermore, these phenomena can greatly change with the rock type, the earthquake magnitude and the observation distance from the fault. Within a distance of a few fault lengths from the epicenter, an earthquake can alter both
the regional stress field and the hydraulic properties of the rocks, influencing the underground fluid distribution. In this thesis, I apply the numerical simulator TOUGH2 to represent the changes in water level of some wells after
the ML 5.9 earthquake that took place in Italy in 2012. The model shows that the wells response to the seismic event can be represented imposing a static stress change and highlights the role of the soil stratigraphy. This zone is also well known for localized methane seepages associated with anomalous soil temperatures. I simulate the process and draw some conclusions on the nature of this phenomenon and on the possible interactions with the local seismicity. Finally, I study the earthquake-fluid interaction from the opposite point of view: looking at how fluids can promote seismicity. I present the results obtained by coupling the TOUGH2 geothermal simulator with a stochastic seed model of seismicity. The coupled simulation could capture the main characteristics of the seismicity induced by the fluid injection in a seismically active area.L'interazione tra terremoti e fluidi crostali è un argomento molto complesso per via dei numerosi meccanismi che sono coinvolti e che si influenzano a vicenda.
Alcuni fenomeni, come l'alterazione delle sorgenti e del flusso di fluidi, la liquefazione e il cambiamento del livello d'acqua nei pozzi freatici, sono largamente documentati in letteratura, tuttavia la loro spiegazione non è ancora del tutto chiara. Oltretutto, questi fenomeni possono cambiare sensibilmente in base al tipo di roccia, alla magnitudo del terremoto e alla distanza dalla faglia. Entro una distanza di poche lunghezze di faglia dall'epicentro, un terremoto può modificare sia il campo di sforzo regionale che le proprietà idrauliche della roccia, influenzando la distribuzione dei fluidi nel sottosuolo. In questa tesi utilizzo il simulatore numerico TOUGH2 per rappresentare la variazione del livello d'acqua di alcuni pozzi successivamente al terremoto di magnitudo ML5.9 che avvenne in Italia nel 2012. Il modello mostra che la risposta dei pozzi al terremoto può essere rappresentata imponendo una variazione di stress statico ed evidenzia l'importanza della stratigrafia del sottosuolo. Questa zona è ben nota anche per emissioni di metano localizzate, associate a riscaldamenti anomali del sottosuolo. In questa tesi presento delle simulazioni per rappresentare questo processo e traggo alcune conclusioni circa la natura di questo fenomeno e sulle sue possibili interazioni con la sismicità locale. In ultimo, studio la relazione tra fluidi e terremoto dal punto di vista opposto: come I fluidi possono facilitare la sismicità. Presento i risultati ottenuti accoppiando il simulatore geotermico TOUGH2 con un modello sismico, stocastico, a “seed”. La simulazione accoppiata è in grado di catturare le caratteristiche principali della sismicità indotta dall'iniezione di fluidi in un'area sismicamente attiva
Modeling hydrothermal system: deriving observables and hydrothermal instability in volcanic and non-volcanic setting
No full textHydrothermal fluids are a fundamental resource for understanding and monitoring volcanic and non-volcanic systems. This thesis is focused on the study of hydrothermal system through numerical modeling with the geothermal simulator TOUGH2. Several simulations are presented, and geophysical and geochemical observables, arising from fluids circulation, are analyzed in detail throughout the thesis. In a volcanic setting, fluids feeding fumaroles and hot spring may play a key role in the hazard evaluation. The evolution of the fluids circulation is caused by a strong interaction between magmatic and hydrothermal systems. A simultaneous analysis of different geophysical and geochemical observables is a sound approach for interpreting monitored data and to infer a consistent conceptual model. Analyzed observables are ground displacement, gravity changes, electrical conductivity, amount, composition and temperature of the emitted gases at surface, and extent of degassing area. Results highlight the different temporal response of the considered observables, as well as the different radial pattern of variation. However, magnitude, temporal response and radial pattern of these signals depend not only on the evolution of fluid circulation, but a main role is played by the considered rock properties. Numerical simulations highlight differences that arise from the assumption of different permeabilities, for both homogeneous and heterogeneous systems. Rock properties affect hydrothermal fluid circulation, controlling both the range of variation and the temporal evolution of the observable signals. Low temperature fumaroles and low discharge rate may be affected by atmospheric conditions. Detailed parametric simulations were performed, aimed to understand the effects of system properties, such as permeability and gas reservoir overpressure, on diffuse degassing when air temperature and barometric pressure changes are applied to the ground surface. Hydrothermal circulation, however, is not only a characteristic of volcanic system. Hot fluids may be involved in several mankind problems, such as studies on geothermal engineering, nuclear waste propagation in porous medium, and Geological Carbon Sequestration (GCS). The current concept for large-scale GCS is the direct injection of supercritical carbon dioxide into deep geological formations which typically contain brine. Upward displacement of such brine from deep reservoirs driven by pressure increases resulting from carbon dioxide injection may occur through abandoned wells, permeable faults or permeable channels. Brine intrusion into aquifers may degrade groundwater resources. Numerical results show that pressure rise drives dense water up to the conduits, and does not necessarily result in continuous flow. Rather, overpressure leads to new hydrostatic equilibrium if fluids are initially density stratified. If warm and salty fluid does not cool passing through the conduit, an oscillatory solution is then possible. Parameter studies delineate steady-state (static) and oscillatory solutions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Studio dei processi vulcanici tramite simulazione numerica: un'applicazione al sistema geotermale di Vulcano (Isole Eolie)
No full textDottorato di ricerca in scienze della terra. 7. ciclo. Tutore F. Barberi. Coordinatore M. TongiorgiConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal
La catastrofe che non ti aspetti
No full textAlcune eruzioni hanno cambiato la storia della vulcanologia, altre il mondo. Tutte sollecitano un’analisi delle catastrofi che prescinda dal qui e ora.Published24-292TM. Divulgazione ScientificaN/A or not JC
Caldera’s Breathing: Poroelastic Ground Deformation at Campi Flegrei (Italy)
No full textGround deformation at Campi Flegrei has fuelled a long-term scientific debate about its driving mechanism and its significance in hazard assessment. In an active volcanic system hosting a wide hydrothermal circulation, both magmatic and hydrothermal fluids could be responsible, to variable degrees, for the observed ground displacement. Fast and large uplifts are commonly interpreted in terms of pressure or volume changes associated with magma intrusion, while minor, slower displacement can be related to shallower sources. This work focuses on the deformation history of the last 35 years and shows that ground deformation measured at Campi Flegrei since 1985 is consistent with a poroelastic response of a shallow hydrothermal system to changes in pore pressure and fluid content. The extensive literature available for Campi Flegrei allows constraining system geometry, properties, and conditions. Changes in pore pressure and fluid content necessary to cause the observed deformation can then be calculated based on the linear theory of poroelasticity. The predicted pore pressure evolution and fluid fluxes are plausible and consistent with available measurements and independent estimates.Published7026654V. Processi pre-eruttiviJCR Journa
Conoscenza (in)utile: società, natura e sapere scientifico
No full textLa conoscenza dei fenomeni naturali permette di elaborare strategie di mitigazione. Ma a volte non basta. Come rendere efficace il sapere scientifico?Published36-402TM. Divulgazione ScientificaN/A or not JC
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