Reconstruction of volcano-tectonic processes in interplay with sedimentary deposition in the Gulf of Naples (Italy) using a seismoacoustic dataset

The Campi Flegrei caldera (CFc) has been considered as one of the world's most active calderas, proven by recent episodes of unrest. As a future eruption could affect nearly 2.5 million people, understanding eruption mechanisms and dynamics is of paramount importance to reliably assess volcanic hazards and risks. In this thesis, the offshore sector of the CFc is investigated based on high-resolution multichannel reflection seismic data, including the first semi-3D multichannel seismic survey of a large collapse caldera. The main outcomes of the current thesis are presented in three novel and comprehensive evolutionary models addressing (1) a 3D reconstruction of the tectono-sedimentary variability in the Gulf of Naples half-graben with respect to volcanism during the past one million years, (2) the conceptual formation of the Campi Flegrei nested-caldera complex, and (3) the 3D post-caldera evolution of the CFc. These findings represent a significant advancement towards understanding the genesis and evolution of the CFc as well as the tectonic formation of the Gulf of Naples half-graben basin and its influence on volcanism

Volcanic Unrest and Pre-eruptive Processes: A Hazard and Risk Perspective

Volcanic unrest is complex and capable of producing multiple hazards that can be triggered by a number of different subsurface processes. Scientific interpretations of unrest data aim to better understand (i) the processes behind unrest and their associated surface signals, (ii) their future spatio-temporal evolution and (iii) their significance as precursors for future eruptive phenomena. In a societal context, additional preparatory or contingency actions might be needed because relationships between and among individuals and social groups will be perturbed and even changed in the presence of significant uncertainty. Here we analyse some key examples from three international and multidisciplinary projects (VUELCO, CASAVA and STREVA) where issues around the limits of volcanic knowledge impact on volcanic risk governance. We provide an overview of the regional and global context of volcanic unrest and highlight scientific and societal challenges with a geographical emphasis on the Caribbean and Latin America. We investigate why the forecasting of volcanic unrest evolution and the exploitability of unrest signals to forecast future eruptive behaviour and framing of response protocols is challenging, especially during protracted unrest. We explore limitations of current approaches to decision-making and provide suggestions for how future improvements can be made in the framework of holistic volcanic unrest risk governance. We investigate potential benefits arising from improved communication, and framing of warnings around decision-making timescales and hazard levels

High Resolution Attenuation Images From Active Seismic Data: The Case Study of Solfatara Volcano (Southern Italy)

<p>The anelastic attenuation of rocks strongly depends on the contained fluid physical state and saturation. Furthermore, it is more sensitive than elastic parameters to changes in the physical state of materials. In a geologically complex  volcanic context, where fluids play a very important role, anelastic imaging of the subsoil is therefore a very powerful tool for a better understanding of its dynamics.</p><p>In this study we present a robust workflow aimed at retrieve accurate 1-D and 3-D anelastic models from the processing of active seismic data, in terms of lateral and depth variations of P-wave quality factors Q<sub>P</sub>. This methodology has been applied to data collected during a high resolution active seismic experiment in a very small-scale volcanic volume, the Solfatara crater, within Campi Flegri caldera, Southern Italy. The presented methodology is developed in three distinct steps: 1) the active seismic data have been properly processed and analyzed for measuring the t* attenuation parameter for all possible source-receivers couples. First, the source contribution has been removed by cross-correlating the recorded signal with the sweep function of the Vibroseis, which was the adopted active seismic source. Then, the spectral decay method has been applied in order to compute the t* values. 2) A reference 1-D attenuation model has been retrieved by means of a grid search procedure aiming at finding the 1-D Qp structure that minimizes the residual between the average observed t* and the theoretical t* distributions. The obtained starting reference model allowed to build a preliminary map of t* residuals through which the retrieved t* dataset has been validated. 3) The 15,296 t* measurements have been inverted by means of a linearized, perturbative approach, in a 160 x 160 x 45 m<sup>3 </sup>tomographic grid.</p><p>The retrieved 3-D attenuation model describes the first 30 m depths of Solfatara volcano as composed of very high attenuating materials, with Qp values ranging between 5 and 40. The very low Qp values, correlated with low Vp values retrieved by a previous tomographic work carried out in the area, indicate the low consolidation degree of very superficial volcanic materials of Solfatara volcano. Finally, in the NE part of the crater, lower attenuating bodies have been imaged: it is a further hint for characterizing this area of the volcano as the shallow release of the CO<sub>2 </sub>plume through the main fumaroles of the crater.</p&gt

Tracking Space and Time Changes of Physical Properties in Complex Geological Media

An important issue in seismology concerns the characterization of the propagation medium, aiming to analyze the behavior of rocks in relation to the generation of earthquakes (both natural and human-made). The basic idea is that seismic waves can be used to image the medium’s physical properties. In this context we placed our research project, concerning the reconstruction of the spatial and temporal changes of physical properties (velocity, attenuation, rock parameters) in complex geological media. In the first part of this thesis we present a detailed description of known and new methodologies useful to track the seismicity, the propagation medium’s features and their temporal variation. In particular, a new rock modelling approach is constructed, allowing the conversion of velocity and attenuation values in rock micro-parameters; and a new equalization procedure for the 4D tomography is developed, allowing at once to optimize the choice of time-windows in the case of massive data-sets and to completely handle seismic tomography issues. In the second part, we show the results obtained by applying this methodologies to three complex areas: the Irpinia fault zones, The Geysers geothermal area and the Solfatara volcano. The relevance of these three areas lies not only in their different physical nature, but also in their different dimension. The obtained results show how the described methodologies can be used in seismogenic and volcanic areas to improve the knowledge of the medium’s properties, in order to mitigate the risk associated to destructive events, and in geothermal areas, to monitor the induced seismicity through the tracking of the medium properties’ temporal variation. Therefore, this thesis represents a useful tool for the characterization of the propagation medium, by providing a compendium of different methodologies and by showing the results of their application to three complex areas characterized by different physical nature and dimensional scale

Probabilistic volcanic hazard assessment for pyroclastic density currents from pumice cone eruptions at Aluto Volcano, Ethiopia

Aluto volcano, in the Main Ethiopian Rift, is a peralkaline caldera system, which comprises conglomerations of rhyolite (obsidian) lavas and enigmatic pumice cones. Recent work at Aluto has found that pumice cone eruptions are highly unsteady, and form convective eruption plumes that frequently collapse to generate pyroclastic density currents (PDCs). We develop a methodology and present results for the first probabilistic volcanic hazard assessment (PVHA) for PDCs at a pumice cone volcano. By doing so, we estimate the conditional probability of inundation by PDCs around Aluto volcano, incorporating the aleatory uncertainty in PDC hazard. We employ a Monte Carlo energy cone modeling approach, which benefits from parameterization informed by field investigations and volcanic plume modeling. We find that despite the relatively modest eruptions that are likely to occur, the wide distribution of past vent locations (and thus the high uncertainty of where future vents might open), results in a broad area being potentially at risk of inundation by PDCs. However, the aleatory uncertainty in vent opening means that the conditional probabilities are lower (≤ 0.12), and more homogeneous, over the hazard domain compared to central-vent volcanoes (where conditional probabilities are often ≤ 1 close to the vent). Despite this, numerous settlements, amenities, and economically valuable geothermal infrastructure, lie within the most hazardous (P(PDC|eruption) ≥ 0.05) regions of Aluto caldera. The Monte Carlo energy cone modeling approach provides a quantitative, accountable and defendable background and long-term PVHA for PDCs from Aluto. These results could be combined in the future with hazard assessments relating to tephra fall and/or lava to develop a comprehensive volcanic hazard map for the caldera. Following appropriate parameterization, the approach developed here can also be used to compute a PDC PVHA at other volcanoes where vent location is uncertain

Pre-eruptive magmatic processes triggering two different size eruptions occurred in recent volcanic activity of the Phlegraean district and their timescales

Pre-eruptive magmatic processes triggering two different size eruptions occurred in recent volcanic activity of the Phlegraean district and their timescale

A Methodology for a Comprehensive Probabilistic Tsunami Hazard Assessment: Multiple Sources and Short-Term Interactions

We propose a methodological approach for a comprehensive and total probabilistic tsunami hazard assessment (TotPTHA), in which many different possible source types concur to the definition of the total tsunami hazard at given target sites. In a multi-hazard and multi-risk perspective, the approach allows us to consider all possible tsunamigenic sources (seismic events, slides, volcanic eruptions, asteroids, etc.). In this respect, we also formally introduce and discuss the treatment of interaction/cascade effects in the TotPTHA analysis and we demonstrate how the triggering events may induce significant temporary variations in short-term analysis of the tsunami hazard. In two target sites (the city of Naples and the island of Ischia in Italy) we prove the feasibility of the TotPTHA methodology in the multi-source case considering near submarine seismic sources and submarine mass failures in the study area. The TotPTHA indicated that the tsunami hazard increases significantly by considering both the potential submarine mass failures and the submarine seismic events. Finally, the importance of the source interactions is evaluated by applying a triggering seismic event that causes relevant changes in the short-term TotPTHA