ALBERT

Description: No abstract

Description: Published

Description: 92-117

Description: 4V. Vulcani e ambiente

Description: restricted

Description: In this work, we tackle the problem of seismic hazard at Etna deriving from the recurrent seismogenic activity of local faults, by adopting two independent methods based on probabilistic approaches. We assess the hazard in terms of macroseismic intensity and represent the occurrence probability calculated for different exposure times both on maps and at fault scale. Seismic hazard maps obtained by applying the “site approach” through the SASHA code and a new probabilistic attenuation model, indicate the eastern flank of the volcano as the most hazardous, with expected intensity (Iexp) in 50 years (i.e. the standard exposure time adopted in the seismic regulations) ranging from degrees IX to X EMS. In shorter exposure periods (20, 10, 5 years), values of Iexp up to IX are also reached in the same area, but they are clearly determined by the earthquakes generated by the Timpe fault system. In order to quantify the contribution of local seismogenic sources to the hazard of the region, we reconstruct the seismic history of each fault and calculate with SASHA the probability that earthquakes of a given intensity may be generated in different exposure times. Results confirm the high level of hazard due to the S. Tecla, Moscarello and Fiandaca faults especially for earthquakes of moderate intensity, i.e. VI≤I0≤VII, with probabilities respectively exceeding 50% and 20% in 10 years, and 30% and 10% in 5 years. Occurrence probability of major events (I0≥VIII) at the fault scale has also been investigated by statistics on intertimes. Under stationary assumptions we obtain a probability of 6.8% in 5 years for each structure; by introducing the time-dependency (time elapsed since the last event occurred on each fault) through a BPT model, we identify the Moscarello and S. Tecla faults as the most probable sources to be activated in the next 5 years (2013–2017). This result may represent a useful indication to establish priority criteria for actions aimed at reducing seismic risk at a local scale.

Description: Published

Description: 158-169

Description: 4.2. TTC - Modelli per la stima della pericolosità sismica a scala nazionale

Description: JCR Journal

Description: reserved

Description: We investigated the seismic potential of a given set of faults in the Etna region, by analysing the inter-event times of major earthquakes as given by the earthquake catalogue. Among the active structures of the volcano, the Timpe fault system in the eastern flank is responsible for the largest earthquakes occurring in historical time, with long-term behaviour characterised by earthquake rates of ~ 20 years for severe/destructive events (epicentral intensity I0 ≥ VIII EMS). By means of coseismic effect analyses and thanks to the peculiarity of earthquake source in this volcanic district, we associated the seismic events to the individual seismogenic sources, obtaining the seismic history of each fault. Mean recurrence time of major events referred to a specific fault can therefore be defined. Then, we calculated the probabilities of occurrence of destructive events both with Poisson and Brownian Passage Time (BPT) models. A time-dependent BPT distribution function has been used to calculate the conditional occurrence probability for each structure of the Timpe seismogenic zone. In a memoryless perspective, the probability of having a major earthquake on individual faults is about 7% in 5 years, while it changes from fault to fault if the probability is conditioned to the time elapsed since the last event. As a result, impending earthquakes are expected on the S. Tecla fault (11%), and on Moscarello and Fiandaca faults (~ 6-9%), all involved in the complex dynamics of the eastern flank of Mt. Etna. These results are consistent with those independently obtained through the site approach, calculated by the SASHA code.

Description: Funding provided by the Italian Presidenza del Consiglio dei Ministri - Dipartimento della Protezione Civile (DPC), project V4 Flank.

Description: Published

Description: 75-88

Description: 3.1. Fisica dei terremoti

Description: JCR Journal

Description: reserved

Description: I modelli di pericolosità sismica tradizionali utilizzano ipotesi semplificate di distribuzione omogenea della sismicità nello spazio, e stazionaria nel tempo. Negli ultimi decenni, grazie anche ad una aumentata disponibilità di osservazioni geologiche e paleosismologiche, stanno prendendo rilievo modelli più strettamente collegati alla fagliazione sismogenetica, che tengano in considerazione anche le variazioni temporali legate al ciclo sismico. In Italia, queste applicazioni sono prevalentemente a carattere metodologico ed esplorativo, dato che solo un limitatissimo numero di strutture sismogenetiche dispone di dati osservativi indispensabili per questo tipo di analisi (ad es. Pace et al., 2006; Peruzza, 2006; Peruzza et al., 2008). Tra queste, le faglie etnee rappresentano un caso di studio particolare per entità, tipologia e frequenza della fagliazione superficiale e della sismicità associata (Azzaro, 1999). Per tale motivo, nell’ambito del progetto DPC V4-Flank finalizzato alla valutazione dell’hazard connesso alla dinamica di fianco all’Etna, abbiamo applicato ai principali sistemi di faglie attive dell’edificio vulcanico, le tecniche di stima dell’hazard basate sulle ipotesi di terremoto caratteristico e dipendenza temporale dall’ultimo evento. A partire dal modello sismotettonico (Azzaro, 2004) e dal catalogo sismico di riferimento (CMTE, Azzaro et al., 2000, 2002, 2006), sono state analizzate le sequenze di eventi sismici attribuibili alle diverse strutture sismogenetiche e ricostruite le loro storie sismiche. Una caratteristica comune nello stile di rilascio sismico di molte faglie è la presenza di terremoti maggiori e minori alternati nel tempo, in una sorta di cicli sismici intervallati da brevi periodo di ritorno (decine di anni) (Fig. 1 in alto). E’ evidente, per alcune strutture sismogenetiche contigue, anche la loro attivazione alternata nel tempo (Fig. 1 in basso). Per ogni singola faglia sono stati quindi verificati i possibili modelli di occorrenza applicando distribuzioni diverse in accordo con ipotesi stazionarie o time-dependent (Fig. 2). I risultati preliminari suggeriscono una certa periodicità degli eventi maggiori associati alle diverse strutture, rappresentata dal coefficiente di variazione sul dataset degli intertempi. Dal momento che le stime di hazard sismico variano in relazione al diverso tempo trascorso dall’ultimo terremoto su ciascuna struttura, applicando un processo con memoria attraverso una funzione di distribuzione del tipo BPT, è stato calcolato l’incremento o la diminuzione della probabilità di un successivo evento sismico, rispetto alle ipotesi poissoniane. Gli sviluppi previsti sono mirati a comprendere anche il ruolo delle strutture sismogenetiche analizzate nei processi geodinamici locali.

Description: Published

Description: Trieste

Description: 3.2. Tettonica attiva

Description: open

Description: The space time inter-event time (IET) distributions of earthquakes occurring from 1988 to 2011 at Mt. Etna are analysed in order to identify the periodicity or stationary behaviour of seismicity, and to correlate it with the volcano-tectonic features of the region. The comparison between IET distributions at Etna with those obtained both for Sicily and Italy, shows that IETs at a larger scale are well-modelled by a gamma distribution, whereas at Etna local scale they are characterised by a bimodal curve, in which the two peaks are related to: (i) the contribution of local seismic swarms with very short inter-event times, and (ii) the background regional stationary seismicity. IET analysis is an important tool to investigate the behaviour of seismicity at different crustal levels in the Etna region, distinguishing sectors that are influenced by volcano dynamics or regional tectonics. Indeed, the spatial variation of IET distributions, obtained by analysing different Etna crustal sectors, shows that seismicity shallower than 5 km is almost entirely characterised by short inter-event times and is mainly confined to the summit area. For earthquakes deeper than 5 km occurring in the eastern flank of the volcano, as well as in eastern Sicily, IET distributions are characterised by independent events which suggest that both areas are influenced by the same extensional regional regime. By contrast, IET distributions obtained for the western flank and northwestern Sicily are marked by two peaks, indicating that the compressional stress is acting in both areas.

Description: Published

Description: 1-9

Description: 2V. Dinamiche di unrest e scenari pre-eruttivi

Description: JCR Journal

Description: restricted

Description: Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the most important greenhouse gas after carbon dioxide. It has recently been established that geogenic gases contribute significantly to the natural CH4 flux to the atmosphere (Etiope et al., 2008). Volcanic/geothermal areas contribute to this flux, being the site of widespread diffuse degassing of endogenous gases (Chiodini et al., 2005). In such an environment soils are a source rather than a sink for atmospheric CH4 (Cardellini et al., 2003; Castaldi and Tedesco, 2005; D’Alessandro et al., 2009; 2011; 2013). Due to the fact that methane soil flux measurements are laboratory intensive, very few data have been collected until now in these areas. Preliminary studies (Etiope et al., 2007) estimated a total CH4 emission from European geothermal and volcanic systems in the range 4-16 kt a-1. This estimate was obtained indirectly from CO2 or H2O output data and from CO2/CH4 or H2O/CH4 values measured in the main gaseous manifestations. Such methods, although acceptable to obtain order-of-magnitude estimates, completely disregard possible methanotrophic activity within the soil. At the global scale, microbial oxidation in soils contributes for about 3-9% to the total removal of methane from the atmosphere. But the importance of methanotrophic organisms is even larger because they oxidise the greatest part of the methane produced in the soil and in the subsoil before its emission to the atmosphere. Environmental conditions in the soils of volcanic/geothermal areas (i.e. low oxygen content, high temperature and proton activity, etc.) have been considered inadequate for methanotrophic microrganisms. But recently, it has been demonstrated that methanotrophic consumption in soils occurs also under such harsh conditions due to the presence of acidophilic and thermophilic Verrucomicrobia. These organisms were found in Italy at the Solfatara di Pozzuoli (Pol et al., 2007), in New Zealand at Hell’s Gate (Dunfield et al., 2007) and in Kamchatka, Russia (Islam et al., 2008). Both the Italian and the Hellenic territories are geodynamically very active with many active volcanic and geothermal areas. Here we report on methane flux measurements made at Pantelleria (Italy) and at Sousaki and Nisyros (Greece). The total methane output of these three systems is about 10, 19 and 1 t a-1, respectively (D’Alessandro et al., 2009; 2011; 2013). The total emissions obtained from methane flux measurements are up to one order of magnitude lower than those obtained through indirect estimations. Clues of methanotrophic activity within the soils of these areas can be found in the CH4/CO2 ratio of the flux measurements which is always lower than that of the respective fumarolic manifestations, indicating a loss of CH4 during the travel of the gases towards earth’s surface. Furthermore laboratory methane consumption experiments made on soils collected at Pantelleria and Sousaki revealed, for most samples, CH4 consumption rates up to 9.50 µg h-1 and 0.52 µg h-1 respectively for each gram of soil (dry weight). Only few soil samples displayed no methane consumption activity. Finally, microbiological and molecular investigations allowed us to identify the presence of methanotrophic bacteria belonging to the Verrucomicrobia and to the Alpha- and Gamma-Proteobacteria in the soils of the geothermal area of Favara Grande at Pantelleria. While the presence of the former was not unexpected due to the fact that they include acidophilic and thermophilic organisms that were previously found in other geothermal environments, the latter are generally considered not adapted to live in harsh geothermal environments. Their presence in the soils of Pantelleria could be explained by the fact that these soils do not have extremely low pH values (〉5). Indeed thermotollerant methanotrophic Gamma-proteobacteria, have been previously found in the sediments of thermal springs in Kamchatka (Kizilova et al., 2012). Such species could find their niches in the shallowest part of the soils of Favara Grande were the temperatures are not so high and they thrive on the abundant upraising hydrothermal methane.

Description: Published

Description: Patras, Greece

Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Description: open

Description: Volcanic and geothermal systems emit endogenous gases by widespread degassing from soils, including CH4, a greenhouse gas twenty-five times as potent as CO2. Recently, it has been demonstrated that volcanic or geothermal soils are not only a source of methane, but are also sites of methanotrophic activity. Methanotrophs are able to consume 10–40 Tg of CH4 a−1 and to trap more than 50% of the methane degassing through the soils. We report on methane microbial oxidation in the geothermally most active site of Pantelleria (Italy), Favara Grande, whose total methane emission was previously estimated at about 2.5Mga−1 (t a−1). Laboratory incubation experiments with three top-soil samples from Favara Grande indicated methane consumption values of up to 59.2 nmol g−1 soil d.w. h−1. One of the three sites, FAV2, where the highest oxidation rate was detected, was further analysed on a vertical soil profile, the maximum methane consumption was measured in the topsoil layer, and values greater than 6.23 nmol g−1 h−1 were still detected up to a depth of 13 cm. The highest consumption rate was measured at 37 C, but a still detectable consumption at 80 C (〉1.25 nmol g−1 h−1) was recorded. The soil total DNA extracted from the three samples was probed by Polymerase Chain Reaction (PCR) using standard proteobacterial primers and newly designed verrucomicrobial primers, targeting the unique methane monooxygenase gene pmoA; the presence of methanotrophs was detected at sites FAV2 and FAV3, but not at FAV1, where harsher chemical–physical conditions and negligible methane oxidation were detected. The pmoA gene libraries from the most active site (FAV2) pointed to a high diversity of gammaproteobacterial methanotrophs, distantly related to Methylocaldum-Metylococcus genera, and the presence of the newly discovered acido-thermophilic Verrucomicrobia methanotrophs. Alphaproteobacteria of the genus Methylocystis were isolated from enrichment cultures under a methane-containing atmosphere at 37 C. The isolates grow at a pH range of 3.5 to 8 and temperatures of 18–45 C, and consume 160 nmol of CH4 h−1 mL−1 of culture. Soils from Favara Grande showed the largest diversity of methanotrophic bacteria detected until now in a geothermal soil. While methanotrophic Verrucomicrobia are reported as dominating highly acidic geothermal sites, our results suggest that slightly acidic soils, in high-enthalpy geothermal systems, host a more diverse group of both culturable and uncultivated methanotrophs.

Description: Published

Description: 5865–5875

Description: 4V. Vulcani e ambiente

Description: JCR Journal

Description: open

Description: Improving the constraints on the atmospheric fate and depletion rates of acidic compounds persistently emitted by non-erupting (quiescent) volcanoes is important for quantitatively predicting the environmental impact of volcanic gas plumes. Here, we present new experimental data coupled with modelling studies to investigate the chemical processing of acidic volcanogenic species during tropospheric dispersion. Diffusive tube samplers were deployed at Mount Etna, a very active open-conduit basaltic volcano in eastern Sicily, and Vulcano Island, a closed-conduit quiescent volcano in the Aeolian Islands (northern Sicily). Sulphur dioxide (SO2), hydrogen sulphide (H2S), hydrogen chloride (HCl) and hydrogen fluoride (HF) concentrations in the volcanic plumes (typically several minutes to a few hours old) were repeatedly determined at distances from the summit vents ranging from 0.1 to 10 km, and under different environmental conditions. At both volcanoes, acidic gas concentrations were found to decrease exponentially with distance from the summit vents (e.g., SO2 decreases from 10 000 μg/m3 at 0.1 km from Etna’s vents down to 7 μg/m3 at 10 km distance), reflecting the atmospheric dilution of the plume within the acid gas-free background troposphere. Conversely, SO2/HCl, SO2/HF, and SO2/H2S ratios in the plume showed no systematic changes with plume aging, and fit source compositions within analytical error. Assuming that SO2 losses by reaction are small during short-range atmospheric transport within quiescent (ash-free) volcanic plumes, our observations suggest that, for these short transport distances, atmospheric reactions for H2S and halogens are also negligible. The one-dimensional model MISTRA was used to simulate quantitatively the evolution of halogen and sulphur compounds in the plume of Mt. Etna. Model predictions support the hypothesis of minor HCl chemical processing during plume transport, at least in cloud-free conditions. Larger variations in the modelled SO2/HCl ratios were predicted under cloudy conditions, due to heterogeneous chlorine cycling in the aerosol phase. The modelled evolution of the SO2/H2S ratios is found to be substantially dependent on whether or not the interactions of H2S with halogens are included in the model. In the former case, H2S is assumed to be oxidized in the atmosphere mainly by OH, which results in minor chemical loss for H2S during plume aging and produces a fair match between modelled and measured SO2/H2S ratios. In the latter case, fast oxidation of H2S by Cl leads to H2S chemical lifetimes in the early plume of a few seconds, and thus SO2 to H2S ratios that increase sharply during plume transport. This disagreement between modelled and observed plume compositions suggests that more in-detail kinetic investigations are required for a proper evaluation of H2S chemical processing in volcanic plumes.

Description: Published

Description: 11653–11680

Description: open

Description: Volcanoes contribute to atmospheric pollution by increasing the amount of reactive and greenhouse gases and aerosols, making volcanic emissions one of the major natural sources of several trace elements to the atmosphere. In particular, Mt. Etna is considered to be, on the long-term average, the major atmospheric point source of many environmental harmful compounds. Their emission occurs in the form of gases, aerosols or particulate, both through continuous passive degassing from open-conduit activity and through sporadic paroxysmal eruptive activity. To estimate the environmental impact of magma-derived trace metals and their depositions processes, five bulk collectors have been deployed at various altitudes on the upper flanks around the summit craters of the volcano. Samples were collected every second week for a period of one year and analyzed for the main chemical-physical parameters (electric conductivity and pH) and for major and trace elements concentrations. The first data obtained clearly show that the volcanic contribution is always prevailing in the sampling site closest to the summit craters (∼1.5 km). In the distal sites (5.5-10 km from the summit) downwind of the summit craters, the volcanic contribution is also detectable but often overwhelmed by anthropogenic or other natural (seawater spray, geogenic dust) contributions. Volcanic contribution may derive from both dry and wet deposition of gases and aerosols from the volcanic plume, but sometimes also from leaching of freshly emitted volcanic ashes. In fact, in our background site (7.5 km in the upwind direction,) volcanic contribution has been detected only following an ash deposition event. Fluorine, S and Cl, are the major elements that prevailingly characterize the volcanic contribution in bulk deposition on Mt. Etna, but high concentrations of many trace elements are also detected in the studied samples. In particular, Si, Al, Fe, Ti, Cu, As, Rb, Pb, Tl, Cd, Cr, U and Ag display, in the site most exposed to the volcanic emissions, median concentration values about two orders of magnitude higher than those measured in our background site. Furthermore some of the analysed elements display very high enrichment values with respect to the average crust and, in the closest site to the summit craters, also deposition values higher than those measured in polluted urban or industrial sites.

Description: Unpublished

Description: Athens, Greece

Description: 4.5. Degassamento naturale

Description: open

Description: Volcanic activity is the main natural sources of sulphur dioxide (SO2) to the atmosphere. Although total anthropogenic sources are overwhelming greater, volcanoes like Mt. Etna and many others are considered to be among the biggest point sources of SO2 also during intereruptive periods. Apart from being one of the most impressive geodynamic expressions, volcanoes are also an important tourist attraction. During the summer season the number of tourists visiting the summit craters each day is on average many tens at Stromboli, hundreds at Vulcano and thousands at Mt. Etna. Of course touristic exploitation of active volcanic areas cannot exempt from warranting a reasonable security to the visiting persons. But while many risks in these areas have been since long time considered, gas hazard, a very subtle risk, is often disregarded. For healthy persons, about 1000 µg m-3 of sulphur dioxide is sensed by smell, 2000 to 4000 µg m-3 cause eye, nose and throat irritation, and 10,000 to 15,000 µg m-3 cause respiratory failure. For individuals with bronchial asthma or lung diseases, exposure to much lower doses could be fatal. Generally, a 700 µg m-3 level is considered to be a safe limit for such persons. The atmospheric concentrations of naturally emitted SO2 were measured at three volcanoes of southern Italy (Mt. Etna, Vulcano and Stromboli). Measurements were made with a network of passive samplers positioned at about 1.5 m above the ground, which gave time-integrated values for periods from few days to 1 month. Samplers were placed in zones of the volcanoes with high tourist frequentation. Measured concentrations reach values as high as 2700, 2400 and 10,000 µg m-3 for Etna, Vulcano and Stromboli respectively. Such values are absolutely dangerous to people affected by bronchial asthma or lung diseases. But considering that these are average values over periods from few days up to one month, SO2 concentrations could reach much higher peak values that could be dangerous also to healthy people. The present study evidences a peculiar volcanic risk connected to the touristic exploitation of active volcanic areas. Such risk is particularly enhanced at Mt.Etna where elderly and not perfectly healthy people can easily reach, with cableway and off-road vehicles, areas with dangerous SO2 concentrations.

Description: Published

Description: Bari, Italy

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Description: open