The Southern Tyrrhenian subduction system shows a complex interaction among asthenospheric flow, subducting slab and overriding plate. To shed light on the deformations and mechanical properties of the slab and surrounding mantle, I investigated seismic anisotropy and attenuation properties through the subduction region. I used both teleseisms and slab earthquakes, analyzing shear-wave splitting on SKS and S phases, respectively. The fast polarization directions φ, and the delay time, δt, were retrieved using the method of Silver and Chan [1991. SKS and S φ reveal a complex anisotropy pattern across the subduction zone. SKS-rays sample primarily the sub-slab region showing rotation of fast directions following the curved shape of the slab and very strong anisotropy. S-rays sample mainly the slab, showing variable φ and a smaller δt. SKS and S splitting reveals a well developed toroidal flow at SW edge of the slab, while at its NE edge the pattern is not very clear. This suggests that the anisotropy is controlled by the slab rollback, responsible for about 100 km slab parallel φ in the sub-slab mantle. The slab is weakly anisotropic, suggesting the asthenosphere as main source of anisotropy. To investigate the physical properties of the slab and surrounding regions, I analyzed the seismic P and S wave attenuation. By inverting high-quality S-waves t* from slab earthquakes, 3D attenuation models down to 300 km were obtained. Attenuation results image the slab as low-attenuation body, but with heterogeneous QS and QP structure showing spot of high attenuation , between 100-200 km depth, which could be due dehydration associated to the slab metamorphism. A low QS anomaly is present in the mantle wedge beneath the Aeolian volcanic arc and could indicate mantle melting and slab dehydration.

Katla is a hazardous volcano in south Iceland, hosting a large caldera covered by the Mýrdalsjökull glacier. The last phreatomagmatic eruption occurred in 1918 and the present repose time is the longest known in history. The 2010 eruption of the neighbouring Eyjafjallajökull volcano prompted scientists’ concerns because the two volcanoes are tectonically connected. No visible eruption occurred, but in July 2011 a 23 hour tremor burst was associated with a glacial flood which caused damage to infrastructure. Deepening of the geothermally fed ice cauldrons, increased earthquake activity within the caldera and new seismicity on the south flank were also observed. Analysis of seismic data, including development of new location strategies, and a geological field study of the south flank were conducted to interpret the seismic sources. The tremor burst consisted of two volcano-related phases originated at the active cauldrons and a third phase generated by the flood. The increased seismicity inside the caldera and evidence of rapid ice melting may indicate that the volcano-related tremor was caused by a subglacial eruption. Alternatively, tremor may have been generated by hydrothermal boiling induced by the flood. The seismicity on the south flank consists of long-period repeating events occurring with regular time intervals, modulated by seasons (higher occurrence in summer). Because of the temporal evolution, hypocentre depth distribution and coincidence with the 2011 unrest, a volcano-related source is considered more likely than a glacial one. Hydrothermal processes may be easier to reconcile with the seasonal pattern than magmatic, although no direct indication of hydrothermal activity was found. A field survey revealed previously unknown flank eruption sites within the south flank. A magmatic source for the seismicity should therefore not be discarded. This observation is of major importance for hazard assessment of the south flank of Katla.

We aim to characterize the rupture dynamics along the subduction zones. We investigated the shear/normal stress coupling when geometrical discontinuities and/or realistic velocity fields induce normal traction perturbations. The Spectral Element Method (SEM) is shown to be a powerful numerical tool to perform dynamic simulations for subduction earthquakes due to its geometrical flexibility and to the easy implementation of classical seismological boundary conditions. Sharp variations of normal stress are induced when a rupture propagates between dissimilar materials. Performing dynamic simulations along bimaterial interfaces, we show how the Coulomb friction law leads to unstable solutions due to the missing time/length scale of shear/normal coupling. We also show how the shear stress response has to be properly delayed to provide stable physical reliable solutions and how this delay can allow to define a length, comparable with the dissipation zone, which can be interpreted as the length of coupling. Free surface interaction is shown to generate a break of symmetry in the shallow part of dipping faults. In particular larger ground motion on the hanging wall and thus larger coseismic slip is evidenced. Due to the fault/free surface interaction this slip is shown to be generally associated with low-frequency radiation. Finally, exploiting these results some dynamic models of Tohoku earthquake are presented. The main source features of that event can be addressed in terms of influence of geometry and structure and thus of shear/normal coupling. Along dip we find a bilateral rupture faster trenchward where the largest coseismic slip is measured. Strong rupture accelerations due to geometrical and velocity discontinuities imply high-frequency sub-sources in the deep part of the subduction. We finally show how taking into account these dynamic features the tsunami scenarios for the Tohoku earthquake lead to higher estimates for tsunami hazard.

In the last years, geodetic measurements have shown that temporal variations in total groundwater content induce transient deformations of the crust that are mostly reflected in the vertical component. Here we present new GPS observations showing a noticeable non-tectonic transient deformation in the Apennines (Italy), mostly evident in the horizontal components, that correlate with multi-annual hydrological signals as measured by rainfall, GRACE (Gravity Recovery and Climate Experiment) and discharge of karst springs. The observed transient signal is superimposed on the long-term ~3mm/yr NE-SW directed active extension, correlates with the seasonal recharge/discharge cycle of groundwater flow and its multi-annual variations and appears to modulate the intensity of tectonic extensional opening in those regions characterized by large carbonate aquifers. In particular, periods of increasing discharge from karstic spring correlate with an enhanced extensional signal, whereas exhaustion periods correlate with reduced extensional signal. Vertical observations, being correlated with GRACE data, reflect the hydrological load variation over regional (European) scale. Horizontal deformations, conversely, affect mostly the sites located near the large carbonate massifs of the Apennines and can't be explained as load induced response. We suggest that the horizontal observed deformation is related to the presence of highly fractured shallow crust that deforms according to variable conditions of the hydraulic head within the large carbonate aquifers. We therefore propose two different models that simulates the effect of a medium permeated with sub-vertical opening fractures. These new findings could contribute to the understanding of the deformation of the large carbonate aquifers and to an improved management of these important natural resources. By focusing on the 2009 L'Aquila earthquake, we finally highlight the difficulties that arise for the estimation of interseimic trends and small tectonic signals in areas affected by such significant non-tectonic deformations.

This work focuses on the role of SAR Interferometry (InSAR) in the study of many phenomena characterizing the Earth's surface. We propose an advanced integration method in order to merge the InSAR data with other geodetic data, i.e. Multiple Aperture Interferometry (MAI), Pixel Offset Tracking (POT) and Global Positioning System (GPS). We apply the method to constrain the full 3D displacement field produced by the Mw 6.1 2014 South Napa Valley earthquake and then we used the results from the integration to perform the source modeling. The first Chapter is meant to introduce the topic of the progressive use of Remote Sensing geodetic data to support the activities of monitoring and hazard mitigation related to natural phenomena. Chapter 2 shows the application of the InSAR technique to reconstruct and model surface displacement fields induced by several phenomena. In Chapter 3, the 3D coseismic displacement map due to the 2014 Mw 6.1 South Napa earthquake, close the San Andreas Fault system (California), is estimated by using a method to merge InSAR and GPS data. InSAR data are provided by the latest satellite of the European Space Agency (ESA), i.e. Sentinel-1, whereas the GPS data were obtained from the BARD network and several online archives. In Chapter 4 we propose an improved algorithm for the data integration and test it on the Napa earthquake. Geodetic data from MAI and POT are added in the processing chain and the GPS data interpolation is modified according to the specific phenomenon. Futhermore, the source modeling is performed by inversion of the obtained 3D displacement component. The best fit is obtained by simulating a fracture in the fault segment in agreement with previous works. Finally, in the last chapter we discuss about the advantages and disadvantages of the data integration and the future perspectives.

The 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.

In recent years, thanks to the technological advances, electromagnetic methods for non-invasive shallow subsurface characterization have been increasingly used in many areas of environmental and geoscience applications. Among all the geophysical electromagnetic methods, the Ground Penetrating Radar (GPR) has received unprecedented attention over the last few decades due to its capability to obtain, spatially and temporally, high-resolution electromagnetic parameter information thanks to its versatility, its handling, its non-invasive nature, its high resolving power, and its fast implementation. The main focus of this thesis is to perform a dielectric site characterization in an efficient and accurate way studying in-depth a physical phenomenon behind a recent developed GPR approach, the so-called early-time technique, which infers the electrical properties of the soil in the proximity of the antennas. In particular, the early-time approach is based on the amplitude analysis of the early-time portion of the GPR waveform using a fixed-offset ground-coupled antenna configuration where the separation between the transmitting and receiving antenna is on the order of the dominant pulse-wavelength. Amplitude information can be extracted from the early-time signal through complex trace analysis, computing the instantaneous-amplitude attributes over a selected time-duration of the early-time signal. Basically, if the acquired GPR signals are considered to represent the real part of a complex trace, and the imaginary part is the quadrature component obtained by applying a Hilbert transform to the GPR trace, the amplitude envelope is the absolute value of the resulting complex trace (also known as the instantaneous-amplitude). Analysing laboratory information, numerical simulations and natural field conditions, and summarising the overall results embodied in this thesis, it is possible to suggest the early-time GPR technique as an effective method to estimate physical properties of the soil in a fast and non-invasive way.

The thesis deals with the Dynamo Theories of the Earth’s Magnetic Field and mainly deepens the turbulence phenomena in the fluid Earth’s core. Indeed, we think that these phenomena are very important to understand the recent decay of the geomagnetic field. The thesis concerns also the dynamics of the outer core and some very rapid changes of the geomagnetic field observed in the Earth’s surface and some aspects regarding the (likely) isotropic turbulence in the Magnetohydrodynamics. These topics are related to the Dynamo Theories and could be useful to investigate the geomagnetic field trends.

Aim of this work is the study of the stress field in the Campi Flegrei caldera during the bradyseismic crisis of 1982-1984. n the first part of the work has been analysed old cretaceous and digital seismic datasets relative to 70th years, and the bradyseismic crisis of 1982-1984 where has been recorded the earthquakes linked to uplifts that interested Campi flegrei caldera during 1969-72 and 1982-84. The seismicity dataset has been used to made some analysis as location and focal mechanisms generation. The focal mechanisms are than analysed using two software to determine the principal state of stress that was predominant in that period. Then, starting from ground deformation data, relative to 1100 optical levelling measure done during the bradyseismic crisis, has been use the inversion method to modelling the source of the deformation. Has been used many model as the Mogi model, the penny shaped-crack, and the rectangular crack of Okada. Consequently, a joint inversion was applicate on ground deformation data and seismicity together to better understand the dynamic of the stress in the area.In the last part of the work, has been determined the excess of pore pressure in the Flegrean area, using focal mechanisms to study the influence of fluid pore pressure on change in the Coulomb stress of the area. Has been used the Coulomb-Navier criterion and Terakawa method (2010) to estimate the excess of pore pressure. Finally, in order to evaluate the reliability of the calculated pore pressures, was done thermo-fluid dynamic simulation and analysed the hydrothermal system of Campi Flegrei caldera. So, has been performed a series of simulation thermo-fluid dynamic injecting a flow in the system varying temperature, pressure and injection rate to model the Campi Flegrei caldera during the unrest.

Orientador: César Augusto Moreira / Banca: Daniel Françoso de Godoy / Banca: José Ricardo Melges Bortolin / Resumo: A expansão urbana desordenada pode gerar graves consequências ao ambiente. A falta de planejamento no escoamento de águas pluviais, aliado à baixa coesão de alguns terrenos pode proporcionar o surgimento de voçorocas, cuja evolução pode resultar em riscos geotécnicos para a população ao redor. Neste sentido, a geofísica possibilita um diagnóstico de produtos da evolução de voçorocas, como o fenômeno de piping, que consiste na geração natural de cavidades no solo. O contraste de resistividade elétrica entre o solo e o espaço vazio da cavidade possibilitam o uso do método da Eletrorresistividade neste tipo de estudo. Este método foi utilizado na investigação de uma voçoroca no município de São Pedro (SP), para a avaliação da continuidade de cavidades formadas por processos de erosão interna ou piping. Foram realizadas 6 linhas paralelas de imageamento elétrico para medidas de resistividade elétrica, com espaçamento de 1m entre eletrodos, de 5m entre linhas, por meio do arranjo Wenner-Schlumberger. A correlação entre dados geofísicos e cavidades revelou uma assinatura geoelétrica de alta resistividade, possivelmente devido à ausência de preenchimento. A integração lateral das seções em mapas de isovalores para a profundidade de ocorrência das cavidades, revela o prolongamento e a ramificação de pipings em porções mais internas do terreno / Abstract: Unorganized urban expansion can result in several consequences to the environment. The absense of planning in the flow of rain water, allied with low cohesion in some terrains can generate gullies, which growing can offer geotechnical risks for the population. By this case, geophysics allows the diagnostic of some products from gully erosion, like the piping phenomena, where natural cavities are formed in the subsoil.The Electrical resistivity contrasts from the soil and the cavities filling material allows the application of Electrorresistivity method. The method was applied in a gully in São Pedro (SP) county to detect cavities formed in a process denominated internal erosion or piping. Were used 6 parallel lines of electrical imaging for the measurement of electrical resistivity values with 84 electrodes and spacing of 1m between each one, 5m between each acquisition line, by the Wenner-Schlumberger array. The results show high resistivity assignature probably due to the absence of filling in the cavities. The lateral integration of the sections in a isovalues map to the depth where occurs the cavities reveals the length and ramifications of the pipings in the internal portions of the terrain / Mestre