Numerical simulations of magma chamber dynamics at Campi Flegrei, and associated seismicity, deformation and gravity changes

Understanding the complex relationships between quantities measured by volcanic monitoring network and shallow magma processes is a crucial headway for the comprehension of volcanic processes and a more realistic evaluation of the associated hazard. This question is very relevant at Campi Flegrei, a volcanic quiescent caldera immediately north-west of Napoli (Italy). The system activity shows a high fumarole release and periodic ground slow movement (bradyseism) with high seismicity. This activity, with the high people density and the presence of military and industrial buildings, makes Campi Flegrei one of the areas with higher volcanic hazard in the world. In such a context my thesis has been focused on magma dynamics due to the refilling of shallow magma chambers, and on the geophysical signals detectable by seismic, deformative and gravimetric monitoring networks that are associated with this phenomenologies. Indeed, the refilling of magma chambers is a process frequently occurring just before a volcanic eruption; therefore, the faculty of identifying this dynamics by means of recorded signal analysis is important to evaluate the short term volcanic hazard. The space-time evolution of dynamics due to injection of new magma in the magma chamber has been studied performing numerical simulations with, and implementing additional features in, the code GALES (Longo et al., 2006), recently developed and still on the upgrade at the Istituto Nazionale di Geofisica e Vulcanologia in Pisa (Italy). GALES is a finite element code based on a physico-mathematical two dimensional, transient model able to treat fluids as multiphase homogeneous mixtures, compressible to incompressible. The fundamental equations of mass, momentum and energy balance are discretised both in time and space using the Galerkin Least-Squares and discontinuity-capturing stabilisation technique. The physical properties of the mixture are computed as a function of local conditions of magma composition, pressure and temperature.The model features enable to study a broad range of phenomenologies characterizing pre and sin-eruptive magma dynamics in a wide domain from the volcanic crater to deep magma feeding zones. The study of displacement field associated with the simulated fluid dynamics has been carried out with a numerical code developed by the Geophysical group at the University College Dublin (O’Brien and Bean, 2004b), with whom we started a very profitable collaboration. In this code, the seismic wave propagation in heterogeneous media with free surface (e.g. the Earth’s surface) is simulated using a discrete elastic lattice where particle interactions are controlled by the Hooke’s law. This method allows to consider medium heterogeneities and complex topography. The initial and boundary conditions for the simulations have been defined within a coordinate project (INGV-DPC 2004-06 V3_2 “Research on active volcanoes, precursors, scenarios, hazard and risk - Campi Flegrei”), to which this thesis contributes, and many researchers experienced on Campi Flegrei in volcanological, seismic, petrological, geochemical fields, etc. collaborate. Numerical simulations of magma and rock dynamis have been coupled as described in the thesis. The first part of the thesis consists of a parametric study aimed at understanding the eect of the presence in magma of carbon dioxide in magma in the convection dynamics. Indeed, the presence of this volatile was relevant in many Campi Flegrei eruptions, including some eruptions commonly considered as reference for a future activity of this volcano. A set of simulations considering an elliptical magma chamber, compositionally uniform, refilled from below by a magma with volatile content equal or dierent from that of the resident magma has been performed. To do this, a multicomponent non-ideal magma saturation model (Papale et al., 2006) that considers the simultaneous presence of CO2 and H2O, has been implemented in GALES. Results show that the presence of CO2 in the incoming magma increases its buoyancy force promoting convection ad mixing. The simulated dynamics produce pressure transients with frequency and amplitude in the sensitivity range of modern geophysical monitoring networks such as the one installed at Campi Flegrei . In the second part, simulations more related with the Campi Flegrei volcanic system have been performed. The simulated system has been defined on the basis of conditions consistent with the bulk of knowledge of Campi Flegrei and in particular of the Agnano-Monte Spina eruption (4100 B.P.), commonly considered as reference for a future high intensity eruption in this area. The magmatic system has been modelled as a long dyke refilling a small shallow magma chamber; magmas with trachytic and phonolitic composition and variable volatile content of H2O and CO2 have been considered. The simulations have been carried out changing the condition of magma injection, the system configuration (magma chamber geometry, dyke size) and the resident and refilling magma composition and volatile content, in order to study the influence of these factors on the simulated dynamics. Simulation results allow to follow each step of the gas-rich magma ascent in the denser magma, highlighting the details of magma convection and mixing. In particular, the presence of more CO2 in the deep magma results in more ecient and faster dynamics. Through this simulations the variation of the gravimetric field has been determined. Afterward, the space-time distribution of stress resulting from numerical simulations have been used as boundary conditions for the simulations of the displacement field imposed by the magmatic dynamics on rocks. The properties of the simulated domain (rock density, P and S wave velocities) have been based on data from literature on active and passive tomographic experiments, obtained through a collaboration with A. Zollo at the Dept. of Physics of the Federici II Univeristy in Napoli. The elasto-dynamics simulations allow to determine the variations of the space-time distribution of deformation and the seismic signal associated with the studied magmatic dynamics. In particular, results show that these dynamics induce deformations similar to those measured at Campi Flegrei and seismic signals with energies concentrated on the typical frequency bands observed in volcanic areas. The present work shows that an approach based on the solution of equations describing the physics of processes within a magmatic fluid and the surrounding rock system is able to recognise and describe the relationships between geophysical signals detectable on the surface and deep magma dynamics. Therefore, the results suggest that the combined study of geophysical data and informations from numerical simulations can allow in a near future a more ecient evaluation of the short term volcanic hazard.

Metamorfismo ercinico di bassa-pressione: evoluzione tettonico-metamorfica del complesso di mandatoriccio (massiccio della Sila - Calabria)

Low-pressure/high-temperature (LP/HT) metamorphic belts are characterised by rocks that experienced abnormal heat flow in shallow crustal levels (T > 600 °C; P < 4 kbar) resulting in anomalous geothermal gradients (60-150 °C/km). The abnormal amount of heat has been related to crustal underplating of mantle-derived basic magmas or to thermal perturbation linked to intrusion of large volumes of granitoids in the intermediate crust. In particular, in this latter context, magmatic or aqueous fluids are able to transport relevant amounts of heat by advection, thus favouring regional LP/HT metamorphism. However, the thermal perturbation consequent to heat released by cooling magmas is responsible also for contact metamorphic effects. A first problem is that time and space relationships between regional LP/HT metamorphism and contact metamorphism are usually unclear. A second problem is related to the high temperature conditions reached at different crustal levels. These, in some cases, can completely erase the previous metamorphic history. Notwithstanding this problem is very marked in lower crustal levels, petrologic and geochronologic studies usually concentrate in these attractive portions of the crust. However, only in the intermediate/upper-crustal levels of a LP/HT metamorphic belt the tectono-metamorphic events preceding the temperature peak, usually not preserved in the lower crustal portions, can be readily unravelled. The Hercynian Orogen of Western Europe is a well-documented example of a continental collision zone with widespread LP/HT metamorphism, intense crustal anatexis and granite magmatism. Owing to the exposure of a nearly continuous cross-section of the Hercynian continental crust, the Sila massif (northern Calabria) represents a favourable area to understand large-scale relationships between granitoids and LP/HT metamorphic rocks, and to discriminate regional LP/HT metamorphic events from contact metamorphic effects. Granulite-facies rocks of the lower crust and greenschist- to amphibolite-facies rocks of the intermediate-upper crust are separated by granitoids emplaced into the intermediate level during the late stages of the Hercynian orogeny. Up to now, advanced petrologic studies have been focused mostly in understanding P-T evolution of deeper crustal levels and magmatic bodies, whereas the metamorphic history of the shallower crustal levels is poorly constrained. The Hercynian upper crust exposed in Sila has been subdivided in two different metamorphic complexes by previous authors: the low- to very low-grade Bocchigliero complex and the greenschist- to amphibolite-facies Mandatoriccio complex. The latter contains favourable mineral assemblages in order to unravel the tectono-metamorphic evolution of the Hercynian upper crust. The Mandatoriccio complex consists mainly of metapelites, meta-arenites, acid metavolcanites and metabasites with rare intercalations of marbles and orthogneisses. Siliciclastic metasediments show a static porphyroblastic growth mainly of biotite, garnet, andalusite, staurolite and muscovite, whereas cordierite and fibrolite are less common. U-Pb ages and internal features of zircons suggest that the protoliths of the Mandatoriccio complex formed in a sedimentary basin filled by Cambrian to Silurian magmatic products as well as by siliciclastic sediments derived from older igneous and metamorphic rocks. In some localities, metamorphic rocks are injected by numerous aplite/pegmatite veins. Small granite bodies are also present and are always associated to spotted schists with large porphyroblasts. They occur along a NW-SE trending transcurrent cataclastic fault zone, which represents the tectonic contact between the Bocchigliero and the Mandatoriccio complexes. This cataclastic fault zone shows evidence of activity at least from middle-Miocene to Recent, indicating that brittle deformation post-dated the Hercynian orogeny. P-T pseudosections show that micaschists and paragneisses of the Mandatoriccio complex followed a clockwise P-T path characterised by four main prograde phases: thickening, peak-pressure condition, decompression and peak-temperature condition. During the thickening phase, garnet blastesis started up with spessartine-rich syntectonic core developed within micaschists and paragneisses. Coevally (340 ± 9.6 Ma), mafic sills and dykes injected the upper crustal volcaniclastic sedimentary sequence of the Mandatoriccio complex. After reaching the peak-pressure condition (≈4 kbar), the upper crust experienced a period of deformation quiescence marked by the static overgrowths of S2 by Almandine-rich-garnet rims and by porphyroblasts of biotite and staurolite. Probably, this metamorphic phase is related to isotherms relaxation after the thickening episode recorder by the Rb/Sr isotopic system (326 ± 6 Ma isochron age). The post-collisional period was mainly characterised by decompression with increasing temperature. This stage is documented by the andalusite+biotite coronas overgrown on staurolite porphyroblasts and represents a critical point of the metamorphic history, since metamorphic rocks begin to record a significant thermal perturbation. Peak-temperature conditions (≈620 °C) were reached at the end of this stage. They are well constrained by some reaction textures and mineral assemblages observed almost exclusively within paragneisses. The later appearance of fibrolitic sillimanite documents a small excursion of the P-T path across the And-Sil boundary due to the heating. Stephanian U-Pb ages of monazite crystals from the paragneiss, can be related to this heating phase. Similar monazite U-Pb ages from the micaschist combined with the lack of fibrolitic sillimanite suggest that, during the same thermal perturbation, micaschists recorded temperatures slightly lower than those reached by paragneisses. The metamorphic history ended with the crystallisation of cordierite mainly at the expense of andalusite. Consequently, the Ms+Bt+St+And+Sill+Crd mineral assemblage observed in the paragneisses is the result of a polyphasic evolution and is characterised by the metastable persistence of the staurolite in the stability fields of the cordierite. Geologic, geochronologic and petrographic data suggest that the thermal peak recorded by the intermediate/upper crust could be strictly connected with the emplacement of large amounts of granitoid magmas in the middle crust. Probably, the lithospheric extension in the relatively heated crust favoured ascent and emplacement of granitoids and further exhumation of metamorphic rocks. After a comparison among the tectono-metamorphic evolutions of the different Hercynian crustal levels exposed in Sila, it is concluded that the intermediate/upper crustal level offers the possibility to reconstruct a more detailed tectono-metamorphic history. The P-T paths proposed for the lower crustal levels probably underestimate the amount of the decompression. Apart from these considerations, the comparative analysis indicates that P-T paths at various crustal levels in the Sila cross section are well compatible with a unique geologic scenario, characterized by post-collisional extensional tectonics and magmas ascent.

Studio dei metodi di valutazione della pericolosità associata ai "debris flow" in ambiente alpino

The present work concerns with the study of debris flows and, in particular, with the related hazard in the Alpine Environment. During the last years several methodologies have been developed to evaluate hazard associated to such a complex phenomenon, whose velocity, impacting force and inappropriate temporal prediction are responsible of the related high hazard level. This research focuses its attention on the depositional phase of debris flows through the application of a numerical model (DFlowz), and on hazard evaluation related to watersheds morphometric, morphological and geological characterization. The main aims are to test the validity of DFlowz simulations and assess sources of errors in order to understand how the empirical uncertainties influence the predictions; on the other side the research concerns with the possibility of performing hazard analysis starting from the identification of susceptible debris flow catchments and definition of their activity level. 25 well documented debris flow events have been back analyzed with the model DFlowz (Berti and Simoni, 2007): derived form the implementation of the empirical relations between event volume and planimetric and cross section inundated areas, the code allows to delineate areas affected by an event by taking into account information about volume, preferential flow path and digital elevation model (DEM) of fan area. The analysis uses an objective methodology for evaluating the accuracy of the prediction and involve the calibration of the model based on factors describing the uncertainty associated to the semi empirical relationships. The general assumptions on which the model is based have been verified although the predictive capabilities are influenced by the uncertainties of the empirical scaling relationships, which have to be necessarily taken into account and depend mostly on errors concerning deposited volume estimation. In addition, in order to test prediction capabilities of physical-based models, some events have been simulated through the use of RAMMS (RApid Mass MovementS). The model, which has been developed by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) in Birmensdorf and the Swiss Federal Institute for Snow and Avalanche Research (SLF) takes into account a one-phase approach based on Voellmy rheology (Voellmy, 1955; Salm et al., 1990). The input file combines the total volume of the debris flow located in a release area with a mean depth. The model predicts the affected area, the maximum depth and the flow velocity in each cell of the input DTM. Relatively to hazard analysis related to watersheds characterization, the database collected by the Alto Adige Province represents an opportunity to examine debris-flow sediment dynamics at the regional scale and analyze lithologic controls. With the aim of advancing current understandings about debris flow, this study focuses on 82 events in order to characterize the topographic conditions associated with their initiation , transportation and deposition, seasonal patterns of occurrence and examine the role played by bedrock geology on sediment transfer.

Portal hypertension: a comparison between portal-venous pressure measurement and ARFI measurement of liver and spleen stiffness

PURPOSE. Portal pressure is measured invasively as Hepatic Venous Pressure Gradient (HVPG) in the angiography room. Liver stiffness measured by Fibroscan was shown to correlate with HVPG values below 12 mmHg. This is not surprising, since in cirrhosis the increase of portal pressure is not directly linked with liver fibrosis and consequently to liver stiffness. We hypothesized that, given the spleen’s privileged location upstream to the whole portal system, splenic stiffness could provide relevant information about portal pressure. Aim of the study was to assess the relationship between liver and spleen stiffness measured by Virtual Touch™ (ARFI) and HVPG in cirrhotic patients. METHODS. 40 consecutive patients (30 males, mean age 62y, mean BMI=26, mean Child-Pugh A6, mean platelet count=92.000/mmc, 19 HCV+, 7 with ascites) underwent to ARFI stiffness measurement (10 valid measurements in right liver lobe both surface and centre, left lobe and 20 in the spleen) and HPVG, blindly to each other. Median ARFI values of 10 samplings on every liver area and of 20 samplings on spleen were calculated. RESULTS. Stiffness could be easily measured in all patients with ARFI, resulting a mean of 2,61±0,76, 2,5±0,62 and 2,55±0,66 m/sec in the liver areas and 3.3±0,5 m/s in the spleen. Median HPVG was 14 mmHg (range 5-27); 28 patients showed values ≥10 mmHg. A positive significant correlation was found between spleen stiffness and HPVG values (r=0.744, p<0.001). No significant correlation was found between all liver stiffness and HVPG (p>0,05). AUROC was calculated to test spleen stiffness ability in discriminating patients with HVPG ≥10. AUROC = 0.911 was obtained, with sensitivity of 69% and specificity of 91% at a cut-off of 3.26 m/s. CONCLUSION. Spleen stiffness measurement with ARFI correlates with HVPG in patients with cirrhosis, with a potential of identifying patients with clinically significant portal hypertension.

Characterization of geothermal reservoirs’ parameters by inverse problem resolution and geostatistical simulations

BTES (borehole thermal energy storage)systems exchange thermal energy by conduction with the surrounding ground through borehole materials. The spatial variability of the geological properties and the space-time variability of hydrogeological conditions affect the real power rate of heat exchangers and, consequently, the amount of energy extracted from / injected into the ground. For this reason, it is not an easy task to identify the underground thermal properties to use when designing. At the current state of technology, Thermal Response Test (TRT) is the in situ test for the characterization of ground thermal properties with the higher degree of accuracy, but it doesn’t fully solve the problem of characterizing the thermal properties of a shallow geothermal reservoir, simply because it characterizes only the neighborhood of the heat exchanger at hand and only for the test duration. Different analytical and numerical models exist for the characterization of shallow geothermal reservoir, but they are still inadequate and not exhaustive: more sophisticated models must be taken into account and a geostatistical approach is needed to tackle natural variability and estimates uncertainty. The approach adopted for reservoir characterization is the “inverse problem”, typical of oil&gas field analysis. Similarly, we create different realizations of thermal properties by direct sequential simulation and we find the best one fitting real production data (fluid temperature along time). The software used to develop heat production simulation is FEFLOW 5.4 (Finite Element subsurface FLOW system). A geostatistical reservoir model has been set up based on literature thermal properties data and spatial variability hypotheses, and a real TRT has been tested. Then we analyzed and used as well two other codes (SA-Geotherm and FV-Geotherm) which are two implementation of the same numerical model of FEFLOW (Al-Khoury model).

Biomimetic Materials for Biomedical Applications

Objects with complex shape and functions have always attracted attention and interest. The morphological diversity and complexity of naturally occurring forms and patterns have been a motivation for humans to copy and adopt ideas from Nature to achieve functional, aesthetic and social value. Biomimetics is addressed to the design and development of new synthetic materials using strategies adopted by living organisms to produce biological materials. In particular, biomineralized tissues are often sophisticate composite materials, in which the components and the interfaces between them have been defined and optimized, and that present unusual and optimal chemical-physical, morphological and mechanical properties. Moreover, biominerals are generally produced by easily traceable raw materials, in aqueous media and at room pressure and temperature, that is through cheap process and materials. Thus, it is not surprising that the idea to mimic those strategies proper of Nature has been employed in several areas of applied sciences, such as for the preparation of liquid crystals, ceramic thin films computer switches and many other advanced materials. On this basis, this PhD thesis is focused on the investigation of the interaction of biologically active ions and molecules with calcium phosphates with the aim to develop new materials for the substitution and repair of skeletal tissue, according to the following lines: I. Modified calcium phosphates. A relevant part of this PhD thesis has been addressed to study the interaction of Strontium with calcium phosphates. It was demonstrated that strontium ion can substitute for calcium into hydroxyapatite, causing appreciable structural and morphological modifications. The detailed structural analysis carried out on the nanocrystals at different strontium content provided new insight into its interaction with the structure of hydroxyapatite. At variance with the behaviour of Sr towards HA, it was found that this ion inhibits the synthesis of octacalcium phosphate. However, it can substitute for calcium in this structure up to 15 atom %, in agreement with the increase of the cell parameters observed on increasing ion concentration. A similar behaviour was found for Magnesium ion, whereas Manganese inhibits the synthesis of octacalcium phosphate and it promotes the precipitation of dicalcium phosphate dehydrate. It was also found that Strontium affects the kinetics of the reaction of hydrolysis of α-TCP. It inhibits the conversion from α-TCP to hydroxyapatite. However, the resulting apatitic phase contains significant amounts of Sr2+ suggesting that the addition of Sr2+ to the composition of α-TCP bone cements could be successfully exploited for its local delivery in bone defects. The hydrolysis of α-TCP has been investigated also in the presence of increasing amounts of gelatin: the results indicated that this biopolymer accelerates the hydrolysis reaction and promotes the conversion of α-TCP into OCP, suggesting that its addition in the composition of calcium phosphate cements can be employed to modulate the OCP/HA ratio, and as a consequence the solubility, of the set cement. II. Deposition of modified calcium phosphates on metallic substrates. Coating with a thin film of calcium phosphates is frequently applied on the surface of metallic implants in order to combine the high mechanical strength of the metal with the excellent bioactivity of the calcium phosphates surface layers. During this PhD thesis, thank to the collaboration with prof. I.N. Mihailescu, head of the Laser-Surface-Plasma Interactions Laboratory (National Institute for Lasers, Plasma and Radiation Physics – Laser Department, Bucharest) Pulsed Laser Deposition has been successfully applied to deposit thin films of Sr substituted HA on Titanium substrates. The synthesized coatings displayed a uniform Sr distribution, a granular surface and a good degree of crystallinity which slightly decreased on increasing Sr content. The results of in vitro tests carried out on osteoblast-like and osteoclast cells suggested that the presence of Sr in HA thin films can enhance the positive effect of HA coatings on osteointegration and bone regeneration, and prevent undesirable bone resorption. The possibility to introduce an active molecule in the implant site was explored using Matrix Assisted Pulsed Laser Evaporation to deposit hydroxyapatite nanocrystals at different content of alendronate, a bisphosphonate widely employed in the treatments of pathological diseases associated to bone loss. The coatings displayed a good degree of crystallinity, and the results of in vitro tests indicated that alendronate promotes proliferation and differentiation of osteoblasts even when incorporated into hydroxyapatite. III. Synthesis of drug carriers with a delayed release modulated by a calcium phosphate coating. A core-shell system for modulated drug delivery and release has been developed through optimization of the experimental conditions to cover gelatin microspheres with a uniform layer of calcium phosphate. The kinetics of the release from uncoated and coated microspheres was investigated using aspirin as a model drug. It was shown that the presence of the calcium phosphate shell delays the release of aspirin and allows to modulate its action.