The analysis of apatite fission tracks is applied to the study of the syn- and post-collisional thermochronological evolution of a vast area that includes the Eastern Pontides, their continuation in the Lesser Caucasus of Georgia (Adjara-Trialeti zone) and northern Armenia, and the eastern Anatolian Plateau. The resulting database is then integrated with the data presented by Okay et al. (2010) for the Bitlis Pütürge Massif, i.e. the western portion of the Bitlis-Zagros collision zone between Arabia and Eurasia. The mid-Miocene exhumation episode along the Black Sea coast and Lesser Caucasus of Armenia documented in this dissertation mirrors the age of collision between the Eurasian and Arabian plates along the Bitlis suture zone. We argue that tectonic stresses generated along the Bitlis collision zone were transmitted northward across eastern Anatolia and focused (i) at the rheological boundary between the Anatolian continental lithosphere and the (quasi)oceanic lithosphere of the Black Sea, and (ii) along major pre-existing discontinuities like the Sevan-Akera suture zone.The integration of both present-day crustal dynamics (GPS-derived kinematics and distribution of seismicity) and thermochronological data presented in this paper provides a comparison between short- and long-term deformation patterns for the entire eastern Anatolia-Transcaucasian region. Two successive stages of Neogene deformation of the northern foreland of the Arabia-Eurasia collision zone can be inferred. (i) Early and Middle Miocene: continental deformation was concentrated along the Arabia-Eurasia (Bitlis) collision zone but tectonic stress was also transferred northward across eastern Anatolia, focusing along the eastern Black Sea continent-ocean rheological transition and along major pre-existing structural discontinuities. (ii) Since Late-Middle Miocene time the westward translation of Anatolia and the activation of the North and Eastern Anatolian Fault systems have reduced efficient northward stress transfer.

La valutazione dei rischi associati all’operatività dei sistemi di stoccaggio, quali la sismicità indotta e la subsidenza, è requisito basilare per una loro corretta gestione e progettazione, e passa attraverso la definizione dell’influenza sullo stato tensionale delle variazioni di pressione di poro nel sottosuolo. Principale scopo di questo progetto è lo sviluppo di una metodologia in grado di quantificare le deformazioni dei reservoir in funzione della pressione di poro, di tarare i modelli utilizzati con casi studio che presentino dati di monitoraggio reali, tali da consentire un confronto con le previsioni di modello. In questa tesi, la teoria delle inomogeneità è stata utilizzata, tramite un approccio semianalitico, per definire le variazioni dei campi elastici derivanti dalle operazioni di prelievo e immissione di fluidi in serbatoi geologici. Estensione, forma e magnitudo delle variazioni di stress indotte sono state valutate tramite il concetto di variazione dello sforzo critico secondo il criterio di rottura di Coulomb, tramite un’analisi numerica agli elementi finiti. La metodologia sviluppata è stata applicata e tarata su due reservoir sfruttati e riconvertiti a sistemi di stoccaggio che presentano dataset, geologia, petrofisica, e condizioni operative differenti. Sono state calcolate le variazioni dei campi elastici e la subsidenza; è stata mappata la variazione di sforzo critico di Coulomb per entrambi i casi. I risultati ottenuti mostrano buon accordo con le osservazioni dei monitoraggi, suggerendo la bontà della metodologia e indicando la scarsa probabilità di sismicità indotta. Questo progetto ha consentito la creazione di una piattaforma metodologica di rapido ed efficace utilizzo, per stimare l’influenza dei sistemi di stoccaggio di gas sullo stato tensionale della crosta terrestre; in fase di stoccaggio, permette di monitorare le deformazioni e gli sforzi indotti; in fase di progettazione, consente di valutare le strategie operative per monitorare e mitigare i rischi geologici associati a questi sistemi. / The assessment of the risks associated with the operations of the storage systems, such as induced seismicity and subsidence, is a basic requirement for their proper management and planning, through the definition of the stress state changes induced by pore pressure variations underground. The main aims of this project is to develop a methodology for the quantification of reservoir deformation as a function of pore pressure, and to calibrate the models used on case studies with real monitoring data, in order to compare the predictions of the models. In this thesis, the theory of inhomogeneities has been used, by means of a semianalytical approach, to define the elastic fields variations induced by fluids withdrawal and injection in geological reservoirs at depth. The failure stress change concept for a Coulomb failure criterion has been used to study the extension, shape and magnitude of in induced stress changes, through the development of finite element numerical analysis. The developed methodology has been applied and calibrated on two case studies of exploited reservoir actually converted to storage systems, which present dataset, geological and petrophysical, and various operating conditions; Elastic fields variations and subsidence are calculated, and Coulomb failure stress changes have been mapped for both case studies. The results show a good agreement with the observations arising from monitoring available on case studies, suggesting the releability of the developed methodology and suggest the low likelihood of induced seismicity. This project led to the creation of a quickly and effectively usable methodological base to estimate the influence of gas storage systems on the stress state of the crust and to monitor deformations and induced stresses; during the design stage, it helps to evaluate the operative strategies for mitigation of geological risks associated with these storage facilities.

The application of two low-temperature thermochronometers [fission-track analysis and (U-Th)/He analyses, both on apatite] to various tectonostratigraphic units of the Menderes and Alanya Massifs of Turkey has provided significant new constraints to the understanding of their structural evolution. The Menderes Massif of western Anatolia is one of the largest metamorphic core complexes on Earth. The integration of the geochronometric dataset presented in this dissertation with preexisting ones from the literature delineates three groups of samples within the Menderes Massif. In the northern and southern region the massif experienced a Late Oligocene-Early Miocene tectonic denudation and surface uplift; whereas data from the central region are younger, with most ages ranging between the Middle-Late Miocene. The results of this study are consistent with the interpretation for a symmetric exhumation of the Menderes Massif. The Alanya Massif of SW Anatolia presents a typical nappe pile consisting of thrust sheets with contrasting metamorphic histories. Petrological and geochronological data clearly indicate that the tectonometamorphic evolution Alanya started from Late Cretaceous with the northward subduction of an ‘Alanya ocean’ under the Tauride plate. As an effect of the closure of the İzmir–Ankara–Erzincan ocean, northward backthrusting during the Paleocene-Early Eocene created the present stacking order. Apatite fission-track ages from this study range from 31.8 to 26.8 Ma (Late Rupelian-Early Chattian) and point to a previously unrecognized mid-Oligocene cooling/exhumation episode. (U-Th)/He analysis on zircon crystals obtained from the island of Cyprus evidentiate that the Late Cretaceous trondhjemites of the Troodos Massif not recorded a significant cooling event. Instead results for the Late Triassic turbiditic sandstones of the Vlambouros Formation show that the Mamonia mélange was never buried enough to reach the closure temperature of the ZHe radiometric system (ca. 200°C), thus retaining the Paleozoic signature of a previous sedimentary cycle.

The object of this work has been the analysis of natural processes controlling the geological evolution of the Montenegro and Northern Albania Continental Margin (MACM) during the Late Quaternary. These include the modern sediment dispersal system and oceanographic regime, the building and shaping of the shelf margin at the scale of 100 kyr and relative to the most recent transition between glacial and interglacial periods. The analysis of the new data shows that the MACM is a shelf-slope system formed by a suite of physiographic elements, including: an inner and an outer continental shelf, separated by two tectonically-controlled morphological highs; a lobated drowned mid-shelf paleodelta, formed during the last sea level fall and low stand; an upper continental slope, affected by gravity-driven instability and a system of extensional faults with surficial displacement, featuring an orientation coherent with the regional tectonics. The stratigraphic study of the MACM shows a clear correspondence between the Late Pleistocene/Holocene mud-wedge and the low reflectivity sectors of the inner shelf. Conversely, most of the outer shelf and part of the continental slope expose deposits from the last sea level low stand, featuring a general sediment starving condition or the presence of a thin postglacial sediments cover. The MACM shows uplift in correspondence of the Kotor and Bar ridges, and subsidence in the outer shelf and upper slope sectors. In fact, seaward of these tectonic ridges, the sparker seismic profile show the presence of four well-defined seismo-stratigraphic sequences, interpreted as forced regression deposits, formed during the last four main glacial phases. In this way, the MACM records the 100 kyr scale sea level fluctuations on its seismo-stratigraphic architecture over the last 350 kyr. Over such time range, through the identification of the paleoshoreline deposits, we estimated an average subsidence rate of about 1.2 mm/yr. / L'obiettivo di questo lavoro è stato quello di analizzare i processi naturali che hanno controllato l'evoluzione del Margine Continentale del Montenegro e dell'albania Settentrionale (MACM) durante il tardo Quaternario. Tali processi includono il sistema attuale di dispersione del sedimento ed il regime oceanografico, la formazione ed il modellamento del margine alla scala dei 100 ka e relativamente all'ultimo periodo di transizione dal glaciale all'interglaciale. L'analisi dei nuovi dati mostra che si tratta di un sistema piattaforma-scarpata caratterizzato da: una piattaforma interna ed una esterna dovesono presenti due alti morfologici a controllo tettonico; un delta lobato relitto attribuito all'ultima fase di caduta del livello marino e una scarpata continentale superiore affetta da processi gravitativi superficiali e da sistemi di faglie estensionali a rigetto superficiale che mostrano un'orientazionecoerente con la tettonica regionale. Lo studio stratigrafico del MACM mostra una chiara corrispondenza tra il cuneo fangoso tardo pleistocenico - olocenico ed i settori a bassa riflettività individuati lungo la piattaforma interna. A differenza, gran parte della piattaforma esterna ed una parte della scarpata continentale mostrano depositi appartenenti all'ultima fase di stazionamento basso del livello marino evidenziando quindi la macanza di sedimentazione o la presenza localizzata di sottili coperture di sedimenti post-glaciali. Il MACM mostra sollevamento in corrispondenza dei ridges di Bar e di Kotor, e subsidenza lungo il settore di piattaforma esterna e scarpata continentale. Infatti, esternamente agli alti tettonici, i profili di sparker mostrano la presenza di quattro sequenze sismo-stratigrafiche ben definite, interpretate come sequenze di regressione forzata messe in posto durante le ultime quattro fasi glaciali. Il MACM registra quindi nella sua successione sismo-stratigrafica le variazioni del livello marino a scala di 100ka durante gli ultimi 350 ka. In questo lasso di tempo, attraverso l'identificazione dei depositi di paleospiaggia, viene effettuata una stima del tasso di subsidenza di circa 1.2 mm/a.

Stratigraphic studies carried out over the last decades in Italy and elsewhere testify a growing interest in Quaternary deposits and in the influence of climate change on their architecture. The subsurface of the Po Plain, in its topmost portion, is made up of alluvial deposits organized in depositional cycles at different scales. This PhD thesis provides millennial-scale stratigraphic reconstruction of the Late Pleistocene-Holocene deposits beneath the southern Po Plain, based on basin-scale correlation of laterally-extensive buried soil horizons. Far from the aim of characterizing palaeosols from a mineralogical and geochemical point of view, we focused on the physical and stratigraphic significance of these horizons. In the Bologna urban area, which hosts an abundance of stratigraphic data, the correlation between seventeen continuously-cored boreholes led to the identification of five vertically-stacked palaeosol-bounded sequences within the 14C time window. In a wide portion of the alluvial plain north of Bologna, far away from the Apenninic margin and from the Po River, where subsurface stratigraphic architecture is dominated by markedly lenticular sediment bodies, palaeosols revealed to be the only stratigraphic marker of remarkable lateral continuity. These horizons are characterized by peculiar resistance values, which make them easily identifiable via pocket penetration tests. Palaeosols reveal specific geometric relationships with the associated alluvial facies associations, allowing reliable estimates of soil development as a function of alluvial dynamics. With the aid of sixty new radiocarbon dates, a reliable age attribution and likely time intervals of exposure were assigned to each palaeosol. Vertically-stacked palaeosols delimitate short-term depositional cycles, likely related to the major episodes of climatic change of the last 40 ky. Through integration of stratigraphic data with 750 archaeological reports from the Bologna area, the impact of human settlements on depositional and pedogenic processes during the late Holocene was investigated. / Le indagini stratigrafiche condotte in Italia e nel mondo negli ultimi decenni testimoniano un crescente interesse per i depositi quaternari e per l’influenza esercitata dalle variazioni climatiche sulla loro architettura. Questa tesi di dottorato si occupa della ricostruzione stratigrafica a scala millenaria dei depositi tardo-pleistocenici e olocenici del Bacino Padano, tra Bologna e il Fiume Po, basata sulla correlazione a scala regionale di orizzonti pedogenizzati lateralmente estesi e persistenti. Lungi dal voler caratterizzare i paleosuoli da un punto di vista mineralogico e geochimico, questo lavoro si focalizza sul significato di questi orizzonti in termini di stratigrafia fisica. Nel sottosuolo della città di Bologna, per il quale è disponibile un’eccezionale densità di dati stratigrafici, la correlazione di diciassette sondaggi a carotaggio continuo ha portato all’individuazione di cinque paleosuoli all’interno della finestra del carbonio 14. Nell’area di pianura a nord di Bologna, lontana dal margine appenninico e dal Fiume Po, caratterizzata nel sottosuolo principalmente da corpi sedimentari a geometria lenticolare, i paleosuoli si sono rivelati gli unici orizzonti guida tracciabili per decine di chilometri all’interno della successione tardo-quaternaria. Questi orizzonti sono caratterizzati da valori elevati di resistenza alla compressione e sono legati alle facies deposizionali di ambiente alluvionale da particolari rapporti geometrici, riflesso di precise relazioni intercorrenti tra pedogenesi e dinamiche alluvionali. Tramite la realizzazione di sessanta datazioni, associate a numerosi dati di letteratura, a ciascun paleosuolo è stata assegnata un’età e un tempo medio di esposizione. Il quadro stratigrafico e cronologico che ne deriva ha permesso l’individuazione di cicli deposizionali a scala sub-milankoviana e la loro correlazione con le variazioni climatiche degli ultimi quarantamila anni. L’integrazione dei dati stratigrafici con 750 relazioni di scavi archeologici, ha permesso, infine, di valutare l’impatto della sempre più diffusa presenza dell’uomo sul territorio bolognese sulla formazione e sul seppellimento dei suoli in età tardo-olocenica.

This work is focused on the analysis of sea–level change (last century), based mainly on instrumental observations. During this period, individual components of sea–level change are investigated, both at global and regional scales. Some of the geophysical processes responsible for current sea-level change such as glacial isostatic adjustments and current melting terrestrial ice sources, have been modeled and compared with observations. A new value of global mean sea level change based of tide gauges observations has been independently assessed in 1.5 mm/year, using corrections for glacial isostatic adjustment obtained with different models as a criterion for the tide gauge selection. The long wavelength spatial variability of the main components of sea–level change has been investigated by means of traditional and new spectral methods. Complex non–linear trends and abrupt sea–level variations shown by tide gauges records have been addressed applying different approaches to regional case studies. The Ensemble Empirical Mode Decomposition technique has been used to analyse tide gauges records from the Adriatic Sea to ascertain the existence of cyclic sea-level variations. An Early Warning approach have been adopted to detect tipping points in sea–level records of North East Pacific and their relationship with oceanic modes. Global sea–level projections to year 2100 have been obtained by a semi-empirical approach based on the artificial neural network method. In addition, a model-based approach has been applied to the case of the Mediterranean Sea, obtaining sea-level projection to year 2050.

In questo lavoro di dottorato sono stati analizzati differenti strumenti impiegati per le stime di pericolosità sismica. Facendo riferimento alla Mappa di Pericolosità Sismica Italiana MPS04 (Gruppo di Lavoro MPS, 2004), redatta dall’Istituto Nazionale di Geofisica e Vulcanologia (INGV) e adottata come mappa di riferimento per il territorio nazionale ai sensi dell’Ordinanza PCM 3519 del 28 aprile 2006, All. 1b, è stato approfondito il calcolo dei tassi di sismicità attraverso la relazione di Gutenberg e Richter (1944). In particolare, si è proceduto attraverso un confronto tra i valori ottenuti dagli autori della Mappa (Gruppo di Lavoro MPS, 2004) e i valori ottenuti imponendo un valore costante e unico al parametro b della relazione (Gutenberg e Richter, 1944). Il secondo tema affrontato è stato l’analisi della presenza di eventi di origine non tettonica in un catalogo. Nel 2000 Wiemer e Baer hanno proposto un algoritmo che identifica e rimuove gli eventi di origine antropica. Alla metodologia di Wiemer e Baer (2000) sono state apportate delle modifiche al fine di limitare la rimozione di eventi naturali. Tale analisi è stata condotta sul Catalogo Strumentale della Sismicità Italiana (CSI 1.1; Castello et al., 2006) e sui cataloghi Europei disponibili online: Spagna e Portogallo, Francia, Nord Europa, Repubblica Ceca, Romania, Grecia. L’ultimo argomento trattato ha riguardato la presunta correlazione tra i meccanismi di fagliazione e il parametro b della relazione di Gutenberg e Richter (1944). Nel lavoro di Schorlemmer et al. (2005), tale correlazione è dimostrata calcolando il b-value su una griglia a scala mondiale raggruppando i terremoti in funzione dell’angolo di rake: i valori maggiori del parametro sono misurati per i terremoti che si originano in un regime distensivo, seguono quelli in un regime trascorrente mentre i valori minori si registrano nelle aree a regime compressivo. Il principale ostacolo per una applicazione del metodo al territorio italiano è rappresentato dal numero ridotto di terremoti per i quali è possibile avere indicazioni circa il meccanismo focale della sorgente: la correlazione è stata così valutata calcolando il b-value all’interno delle zone sismogenetiche definite per la realizzazione di MPS04 (Gruppo di Lavoro MPS, 2004), alle quali è stato nuovamente assegnato un meccanismo di fagliazione prevalente attraverso la somma del tensore momento. Sono inoltre allegati lavori altri lavori prodotti nell’ambito della pericolosità sismica.

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.