Studio preliminare di due sequenze di microterremoti accadute nel 2011 e nel 2012 nell'area dei Monti Iblei Orientali (Sicilia sudorientale - Italia)

Nell’ottobre 2011 e nel giugno 2012 due sequenze sismiche hanno interessato l’area a sud di Canicattini Bagni, sulle propaggini orientali dei Monti Iblei, in Sicilia sudorientale. Le due sequenze, costituite ognuna da più di un centinaio di scosse, sebbene di modesta energia, sono state avvertite con ansia dalla popolazione provocando anche lievi danni nelle località prossime all’area epicentrale. Al fine di monitorare con maggior dettaglio l’evoluzione della sequenza in corso, la rete sismica permanente gestita dall’Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Etneo - Sezione di Catania (INGV-OE) è stata implementata, subito dopo l’inizio della sequenza di ottobre 2011, da due stazioni mobili digitali in registrazione locale. Successivamente, dopo la ripresa dell’attività sismica nel mese di giugno 2012, le due stazioni mobili digitali sono state reinstallate negli stessi siti utilizzati precedentemente per ulteriori circa quaranta giorni. Le due stazioni mobili, durante il loro periodo di funzionamento, hanno permesso di rilevare un elevato numero di microterremoti. In questo lavoro vengono presentati i risultati preliminari relativi alle due sequenze sismiche allo scopo di definire con estremo dettaglio la struttura sismogenetica attivatasi. È attualmente in corso l’integrazione del dataset acquisito dall’INGV-OE nell’ambito delle attività di monitoraggio, con i dati acquisiti dalle due stazioni mobili installate. La peculiarità delle due sequenze consiste nel fatto che esse: i) rappresentano il maggior rilascio energetico, avvenuto nel corso degli ultimi dieci anni, nell’area iblea; ii) testimoniano la presenza di una sorgente sismogenetica superficiale ben distinta dal pattern sismico tipico dell’Altopiano Ibleo

The Borehole Experiment: Investigation of Cortical Structures Through 3D Array Techniques

Over the last few years it is growing the need to monitor the volcanic activity with modern technology in order to mitigate volcanic hazard through the detection of any possible precursor phenomena. The use of high performance seismic stations, such as borehole instruments, may increase the signal to noise ratio (SNR), improving the capability to detect very small signals. Over the past 40 years much attention has been given to the use of seismic arrays to measure the slowness vector of coherent signals. The main advantage of seismic arrays consists in their ability to detect weak or emergent signals, and to allow for an effective noise reduction through multichannel waveform stacking. A reliable prediction of the ray-path back-propagated from the recording site to the source is strongly limited by the poor knowledge of the local shallow velocity structure. Usually in volcanic environments the propagation of seismic signals through the shallow layers is strongly affected by lateral heterogeneity, attenuation, scattering, and interaction with the free surface. Driven by these motivations, on May 2014, in collaboration with the colleagues of Osservatorio Vesuviano (INGV), we deployed a 3D seismic array in the area where the borehole seismic station called Pozzo Pitarrone is installed at a depth of about 130 meters. This will improve our knowledge about: • the structure of the top layer and its relationship with geology; • analysis of the signal to noise ratio (SNR) of volcanic signals as a function of frequency; • study of seismic ray-path deformation caused by the interaction of the seismic waves with the free surface; • evaluation of the attenuation of the seismic signals correlated with the volcanic activity. The results of these analyses will improve the general knowledge of wave propagation in the shallow layers and will give a new contribution to the seismic monitoring of Etna volcano.PublishedNicolosi (Catania), Italy1T. Struttura della Terr

Models of Neutrino Masses and Mixings

We review theoretical ideas, problems and implications of neutrino masses and mixing angles. We give a general discussion of schemes with three light neutrinos. Several specific examples are analyzed in some detail, particularly those that can be embedded into grand unified theories.Comment: 44 pages, 2 figures, version accepted for publication on the Focus Issue on 'Neutrino Physics' edited by F.Halzen, M.Lindner and A. Suzuki, to be published in New Journal of Physics

Seismological constraints for the dyke emplacement of the July-August 2001 lateral eruption at Mt. Etna volcano, Italy

In this paper we report seismological evidence regarding the emplacement of the dike that fed the July 18 - August 9, 2001 lateral eruption at Mt. Etna volcano. The shallow intrusion and the opening of the eruptive fracture system, which mostly occurred during July 12, and July 18, were accompanied by one of the most intense seismic swarms of the last 20 years. A total of 2694 earthquakes (1 £ Md £ 3.9) were recorded from the beginning of the swarm (July 12) to the end of the eruption (August 9). Seismicity shows the upward migration of the dike from the basement to the relatively thin volcanic pile. A clear hypocentral migration was observed, well constraining the upwards propagation of a near-vertical dike, oriented roughly N-S, and located a few kilometers south of the summit region. Earthquake distribution and orientation of the P-axes from focal mechanisms indicate that the swarm was caused by the local stress source related to the dike intrusion

Independent modal control for nonlinear flexible structures: An experimental test rig

This paper investigates the use of independentmodalcontrol to suppress the vibration of nonlinearflexible structures. In recent years technological improvements in the mechanical field have led to high-performance systems with low weight and, as a consequence, high flexibility and low damping. Here active control quickly bettered the traditional passive damping systems. The structure investigated in this paper is a multi-body flexible boom moved by hydraulic actuators. The nonlinear system dynamic was numerically reproduced and a control strategy, based on the use of the same actuators, was developed. Finally a testrig was created to validate the proposed approach experimentally