Monitoring Seismo-volcanic and Infrasonic Signals at Volcanoes: Mt. Etna Case Study     

Andrea Cannata  Giuseppe Di Grazia  Marco Aliotta  Carmelo Cassisi  Placido Montalto  Domenico Patanè 《Pure and Applied Geophysics》2013,170(11):1751-1771

Volcanoes generate a broad range of seismo-volcanic and infrasonic signals, whose features and variations are often closely related to volcanic activity. The study of these signals is hence very useful in the monitoring and investigation of volcano dynamics. The analysis of seismo-volcanic and infrasonic signals requires specifically developed techniques due to their unique characteristics, which are generally quite distinct compared with tectonic and volcano-tectonic earthquakes. In this work, we describe analysis methods used to detect and locate seismo-volcanic and infrasonic signals at Mt. Etna. Volcanic tremor sources are located using a method based on spatial seismic amplitude distribution, assuming propagation in a homogeneous medium. The tremor source is found by calculating the goodness of the linear regression fit (R ²) of the log-linearized equation of the seismic amplitude decay with distance. The location method for long-period events is based on the joint computation of semblance and R ² values, and the location method of very long-period events is based on the application of radial semblance. Infrasonic events and tremor are located by semblance–brightness- and semblance-based methods, respectively. The techniques described here can also be applied to other volcanoes and do not require particular network geometries (such as arrays) but rather simple sparse networks. Using the source locations of all the considered signals, we were able to reconstruct the shallow plumbing system (above sea level) during 2011.  相似文献   

Regimes of magma recharge and their control on the eruptive behaviour during the period 2001–2005 at Mt. Etna volcano     

Carmelo Ferlito  Marco Viccaro  Eugenio Nicotra  Renato Cristofolini 《Bulletin of Volcanology》2012,74(2):533-543

Mount Etna volcano (Italy) during the period 2001–2005 has undergone a period of intense eruptive activity marked by three large eruptions (2001, 2002–2003 and 2004–2005). These eruptions encompassed diverse eruptive styles and regimes: from intensely explosive, during 2001 and 2002–2003 eruptions, to exclusively effusive in the 2004–2005 event. In this work, we put forward the idea that these three eruptions are the response of the progressive arrival into the uppermost segment of the open-conduit system of a new magma, which was geochemically distinct in terms of trace element and Sr–Nd–Pb isotope signature from the products previously emitted by the Etnean volcano. The magma migrated upwards mainly through a peripheral tectonic system, which can be considered as eccentric in spite of its relative proximity to the main system. The ingress of the new magma and its gradual displacement from the eccentric system into the uppermost sector of the open-conduit gave rise to different eruptive behaviours. At the beginning, the ascent of the undegassed magma, able to exsolve a gas phase at depth, and its interaction with closed-system magma reservoirs less than 10 km deep gave rise to the explosive events of 2001 and 2002–2003. Later, when the same magma entered into the open-conduit system, it took part in the steady-state degassing and partially lost its volatile load, leading to a totally effusive eruption during the 2004–2005 event. One further consideration highlighted here is that in 2001–2005, migration of the feeding axis from an eccentric and peripheral position towards the main open-conduit has led to the development of a new vent (South East Crater 2) located at the eastern base of the South East Crater through which most of the subsequent Etnean activity occurred.  相似文献   

Probabilistic Reasoning Over Seismic Time Series: Volcano Monitoring by Hidden Markov Models at Mt. Etna     

Carmelo Cassisi  Michele Prestifilippo  Andrea Cannata  Placido Montalto  Domenico Patanè  Eugenio Privitera 《Pure and Applied Geophysics》2016,173(7):2365-2386

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Spatial distribution of phytoplankton cells in small elongated lakes subject to weak diurnal wind forcing   总被引：1，自引：0，他引：1  

Javier Vidal  Anna Rigosi  Andrea Hoyer  Carmelo Escot  Francisco J. Rueda 《Aquatic Sciences - Research Across Boundaries》2014,76(1):83-99

The horizontal distribution of phytoplankton in a medium-size canyon type reservoir, forced by weak winds of 3–4 ms^?1, is largely driven by the interaction of the large-scale circulation and processes regulating the vertical distribution of algal cells in the water column. These drivers, in turn, are subject to diurnal variations, making our understanding of the horizontal distribution of phytoplankton a challenging task. A three-dimensional physical-–ecological model is used to understand the spatial distribution of algae and the role of diurnal variations in the physical–biological drivers. The model was used to demonstrate that the large-scale circulation induced during the day is more efficient generating patchiness than the circulation existing at night, when convectively driven turbulence homogenizes the upper layers. Different spatial distributions develop for different populations and under different forcing scenarios, characterized in terms of the directionality of wind forcing, wind magnitude and the lags between winds and diel heat fluxes. The time scales needed so that algal biomass in the surface exhibit significant longitudinal gradients—T _P —will vary depending on the algal group, and its ability to regulate its vertical position. These scales are shorter for those species that either migrate actively in the water column or exhibit positive buoyancy (Cryptophytes or Positive buoyant algae). In El Gergal, these scales T _P are on the order of a few days. Synoptic changes in the meteorological forcing, like the passing of a front, could potentially change the longitudinal distribution of algal biomass if they persist for periods of time longer than T _P .  相似文献   

Aliphatic hydrocarbons in metasomatized gabbroic xenoliths from Hyblean diatremes (Sicily): Genesis in a serpentinite hydrothermal system     

Enrico Ciliberto  Carmelo Crisafulli  Fabio Carmelo Manuella  Filippo Samperi  Salvatore Scirè  Vittorio Scribano  Marco Viccaro  Ezio Viscuso 《Chemical Geology》2009,258(3-4):258-268

Many tholeiite gabbro xenoliths from the Hyblean tuff-breccia deposits (Sicily, southern Italy) present mineralogical and geochemical evidence for hydrothermal alteration at different temperatures and water/rock ratios. In some cases, the primary mineral assemblage has been entirely replaced by Na-rich alkali feldspar, chlorite/smectite interlayers, zeolites, aegirine–augite, titanite, zircon etc. Hence the chemical composition of such metasomatic rocks displays larger amounts of volatiles, alkalis, Zr, Hf, U, Th and lower Ca, Mg, Fe with respect to the original gabbro. Five hydrothermally altered gabbroic xenoliths were selected for thermal decrepitation and bulk gas analyses by quadrupole mass spectrometry. All the samples analyzed display the same Electron Impact-Direct Pyrolysis Mass spectra (EI-DPMS). These show a series of peaks differing by 14 mass units due to loss of methylene groups (–CH₂), by a fragmentation process typical of saturated aliphatic and aliphatic–aromatic hydrocarbons. In addition, Fourier Transform Infrared (FT-IR) spectra of the samples present several bands typical of vibration frequencies of aliphatic hydrocarbons. The high-molecular-weight hydrocarbons observed probably originated from Fischer–Tropsch-type (FT-t) synthesis in the high temperature section of a serpentinite-hosted hydrothermal system. This suggestion may lend support to the recent hypothesis regarding the original oceanic nature of the Hyblean lithospheric basement.  相似文献   

Overland flow generation on hillslopes of complex topography: analytical solutions     

Carmelo Agnese  Giorgio Baiamonte  Cecilia Corrao 《水文研究》2007,21(10):1308-1317

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Adaptive optics at short wavelengths     

Guido Agapito  Carmelo Arcidiacono  F. Quirós-Pacheco  Simone Esposito 《Experimental Astronomy》2014,37(3):503-523

The First Light Adaptive Optics (FLAO) system has been successfully commissioned at the Large Binocular Telescope. It delivers extreme adaptive optics performance using bright natural guide stars reaching 90 % Strehl Ratios in H-band. Observations with current adaptive optics systems are limited to the near infrared wavelengths, in these bands the diffraction limited resolution of the largest ground-based telescopes (8–10 meter class) is comparable to the one of the much smaller Hubble Space Telescope that observes in the visible bands. This study aims to demonstrate the feasibility of an adaptive optics system designed to achieve very high order correction at visible wavelengths (0.5 to 0.8 μ m) with significant sky coverage. Upgrading the FLAO design with a low noise CCD relaxes the reference magnitude limit needed to achieve greater performance. In particular, we demonstrate that a gain of 1–2 magnitudes is possible by upgrading the wavefront sensor with a very low read out noise CCD. For future AO systems, in addition to low noise CCDs, deformable (secondary) mirrors with a higher actuator density will be able to move the high order correction capability from the near infrared to the visible wavelengths (Strehl Ratio of 80 % in R (0.7 μ m), 60 % in V (0.5 μ m)). We investigate, by means of numerical simulation, the gain in imaging performance obtained at Near Infrared, Visible, and UV wavelengths. The results of these simulations have been used to derive the empirical relation between Strehl Ratio and magnitude of the reference star and we then use this relationship to perform a detailed sky coverage analysis based on astronomical catalog data. The detailed simulations of the Point Spread Functions allow us to compute Ensquared Energy and Strehl Ratio for the magnitude working range of such an Adaptive Optics system. We present the results of the instrumental isoplanatic angle determination. We then used these values to compute the relationship between correction level and the off-axis angle from the reference star. The Strehl Ratio relationship with the reference magnitude and the angular distance provides the information needed to perform the sky-coverage analysis, which demonstrates that the designed system is able to provide V and R bands correction on a not negligible few percent of the sky.  相似文献   

Composition and geochemistry of clay sediments offshore the northeastern Sicilian coast (Southeastern Tyrrhenian Sea,Italy)     

Carmelo Saccà  Domenica SaccàPreziosa Nucera  Anna De Fazio 《Estuarine, Coastal and Shelf Science》2011

Grain-size, mineralogical and chemical analyses were carried out on fine fraction of sediments collected in the Gulfs of Patti and Milazzo, two borderland basins in the Southern Tyrrhenian extending offshore the northeastern Sicilian coast.  相似文献   

Relationship between the flank sliding of the South East Crater (Mt. Etna, Italy) and the paroxysmal event of November 16, 2006     

Carmelo Ferlito  Marco Viccaro  Eugenio Nicotra  Renato Cristofolini 《Bulletin of Volcanology》2010,72(10):1179-1190

Over the last 2 years, the south east crater (SEC) at Mt. Etna (Italy) has been characterised by the intermittent emission of lava flows, often accompanied by paroxysmal episodes with violent strombolian activity and/or lava fountains. One of the most intense and intriguing episodes occurred on November 16, 2006 during strombolian and effusive activity from the very top of the SEC. At the eastern base of the crater, a violent and short-lasting outburst generated a 300-m-high eruptive curtain of finely fragmented magma and steam, which collapsed in a few seconds giving rise to a small but significant pyroclastic flow. The paroxysm was preceded by progressive sliding of the eastern flank of the SEC edifice, which led to the formation of a large niche. Previously published models explain the outburst as due to rapid vaporisation of water contained in sediments on contact with hot lava flowing along the flank of the SEC or, alternatively, to gravitational collapse of a destabilised portion of the eastern flank of the crater. However, several lines of evidence suggest that these models do not adequately explain the paroxysm, which we propose was associated with the explosive emission of magma during the rapid opening of an ESE-WNW-oriented fracture at the eastern base of the SEC. Moreover, geochemical data of the products associated with this episode show that they are the most primitive and gas-rich among those erupted during the entire 2006 period. We suggest that the paroxysm of November 16, 2006, which occurred at base of the SEC, was a magma outburst due to rapid ground fracturing related to a drop in confining pressure upon the underlying dyke consequent to the sliding of the eastern flank of the SEC cone. Specifically, the unloaded shallow portion of the feeding dyke did not restrain the arrival of a new batch of gas-rich magma, which worked its way out by fracturing the base of the niche at its weakest point. This paroxysm appears significant because it reveals the potential development of syn-eruptive dynamics acting directly on the uppermost portion of the plumbing system which is able to generate pyroclastic flows even on basaltic volcanoes such as Mount Etna.  相似文献   

The dyke swarm of Mount Calanna (Etna, Italy): an example of the uppermost portion of a volcanic plumbing system     

Carmelo Ferlito  Eugenio Nicotra 《Bulletin of Volcanology》2010,72(10):1191-1207

A new multidisciplinary study, combining geology, petrography, and geochemistry, on the rocks of the isolated hill of Mount Calanna (Mount Etna, Italy) has provided evidence for the existence of a dyke swarm, formed by more than 200 dykes distributed over an area of ~0.7 km², with an intensity of intrusion up to 40%. All bodies are deeply altered, and the geological and mesostructural surveying of 132 dykes revealed that they intruded in E–W direction, with an average dip of 60°. The faults affecting the outcrop have in general an E–W strike and dip of ~55°: these have all normal motion and have been interpreted as coeval with the dykes. This interpretation contrasts with the previous hypothesis that considered Mount Calanna as a thrust resulting from compressive deformation resulting from the gravitational spreading of the volcanic edifice. Mount Calanna is here interpreted as the uppermost portion of a vertically extensive magmatic plexus that fed the eruptive activity of one (or more) eruptive center/s sited in the Valle del Bove area. Measurements of the apparent densities on 23 dykes and host rock samples give an average value of 2,420 kg/m³ for the entire complex, ~15% lower than the density expected for hawaiitic magma, placing an important constraint on the geophysical identification of similar structures. Considering that Mount Etna is not an old eroded edifice but an active and growing volcano, the exposure of this subvolcanic structure can be regarded as exceptional. Its geometry and physical characteristics can be thus regarded as an interesting example of the present-day shallow plumbing system of Mount Etna as well as of other basaltic volcanoes.  相似文献