Cognate xenoliths in Mt. Etna lavas: witnesses of the high-velocity body beneath the volcano

Various xenoliths have been found in lavas of the 1763 (“La Montagnola”), 2001, and 2002–03 eruptions at Mt. Etna whose petrographic evidence and mineral chemistry exclude a mantle origin and clearly point to a cognate nature. Consequently, cognate xenoliths might represent a proxy to infer the nature of the high-velocity body (HVB) imaged beneath the volcano by seismic tomography. Petrography allows us to group the cognate xenoliths as follows: i) gabbros with amphibole and amphibole-bearing mela-gabbros, ii) olivine-bearing leuco-gabbros, iii) leuco-gabbros with amphibole, and iv) Plg-rich leuco gabbros. Geobarometry estimates the crystallization pressure of the cognate xenoliths between 1.9 and 4.1 kbar. The bulk density of the cognate xenoliths varies from2.6 to 3.0 g/cm3. P wave velocities (VP), calculated in relation to xenolith density, range from 4.9 to 6.1 km/s. The integration of mineralogical, compositional, geobarometric data, and density-dependent VP with recent literature data on 3D VP seismic tomography enabled us to formulate the first hypothesis about the nature of the HVB which, in the depth range of 3–13 km b.s.l., is likely made of intrusive gabbroic rocks. These are believed to have formed at the “solidification front”, a marginal zone that encompasses a deep region (>5 km b.s.l.) of Mt. Etna’s plumbing system, within which magma crystallization takes place. The intrusive rocks were afterwards fragmented and transported as cognate xenoliths by the volatile-rich and fast-ascending magmas of the 1763 “La Montagnola”, 2001 and 2002–03 eruptions

Double-difference tomography at Mt. Etna volcano

Double-difference tomography at Mt Etna volcano was realized by using the tomographic algorithm developped by Monteiller et al. (2005), in which the travel-time computation was performed using a finite-difference solution of the Eikonal equation (Podvin and Lecomte, 1991) and a posteriori ray-tracing. The inverse problem was solved using a probabilistic approach (Tarantola and Valette, 1982). The optimal a priori information (correlation length and a priori model variance) was found experimentally by performing tomographies for correlation lengths and variances varying in large intervals. This probabilistic approach allowed us to use a sech pdf for representing errors in differential times. Data were travel-times and time delays provided by a set of 329 earthquakes, well-recorded by the INGV-CT seismic network (50 stations) on the Mt Etna volcano during the seismo-volcanic crisis occurring between October 2002 and January 2003. Checkerboard tests realized with this geometry and earthquake pairs showed that the model can be correctly reconstructed in a significant area around Mt Etna volcano. Results of the P and S-wave double-difference tomography clearly evidenced two concentric features: a fast central cylindrical core, probably of intrusive origin, surrounded by a slow annealed body, which could be related to partial melting

Double-difference tomography at Mt Etna volcano: Preliminary results

We performed a preliminary double-difference tomographic study using earthquake data recorded by the INGV-Catania seismic network during the large seismic and eruptive crisis of 2002-2003 at Mt Etna volcano. Compared to previous models, first results presented from the inversion of travel-time differences, tend to show an increase in the velocity contrast between the fast core and the slow periphery of the volcano

Assessing seismic efficiency from scalar Moment-rates: an application to Mt. Etna volcano (Italy)

Here we propose an improved estimation of the scalar seismic (from instrumental and historical catalogues), geodetic and geologic moment-rates for the eastern flank of Mt. Etna. The estimated moment-rates have been compared in terms of seismic efficiency. Results show that all the calculated efficiency values are lower than 40%, i.e., the geodetic moment-rate estimations are generally larger than the seismic and the geologic ones. Although a number of reasons may account for the observed discrepancy, we are confident that a large amount of the deformation affecting the eastern flank occurs aseismically

Multidisciplinary geophysical study of the NE sector of the unstable flank of Etna volcano

On volcanic areas, usually characterized by complex structural environments, a lot of independent geophysical studies are usually performed. The non-uniqueness of the geophysical inverse models, the different level of reso- lution and sensitivity of the results spurred us to integrate independent geophysical datasets and results collected on Mt. Etna volcano, in order to obtain more accurate and reliable model interpretation. Mt. Etna volcano is located along the eastern coast of Sicily and it is characterized by a complex structural set- ting. In this region, the general N-S compressive regime related to the Africa – Europe collision interacts with the WNW-ESE extensional regime associated to the Malta Escarpment dynamics, observable along the eastern coast of Sicily. At Mt Etna, a great number of studies concerns the existence of instability phenomena; a general eastward mo- tion of the eastern flank of the volcano has been measured with always increasing detail and its relationship with the eruptive and magmatic activity is being investigated. The unstable flank appears bounded to the north by the E–W-trending Provenzana - Pernicana Fault System and to the SW by the NS Ragalna Fault system. Eastwards, this area is divided by several NW–SE trending faults. Recent studies consider this area as divided into several blocks characterized by different shape and kinematics. Ground deformation studies (GPS and InSAR) define the NE portion of the unstable flank as the most mobile one. In the frame of the MEDiterranean Supersites Volcanoes (MED-SUV) project, ground deformation data (GPS and INSAR), 3D seismicity, seismic tomography and two resistivity model profiles, have been analyzed together, in order to put some constraints on the deep structure of the NE sector of the unstable flank. Seismic data come from the permanent network run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) - Sezione di Catania, Osservatorio Etneo. Ground deformation data comes from InSAR Permanent Scatterers analyses of different spaceborn sensors. The resistivity models come from a MT survey carried out on the eastern flank of the volcano and consisting of thirty broad-band soundings along N-S and NW-SE oriented profiles. We found that the NE sector of the sliding volume, modeled by ground deformation data inversions and character- ized by the highest displacement velocity, is characterized low resistivity values and it is bounded by two seismic clusters. The northern one is clearly related to the Pernicana fault and it’s not deeper than 3 km b.s.l. while the second one is located southwards, beneath the northern wall of the Valle del Bove, not related to any evident struc- ture at the surface. An evident layer with very reduced seismicity lies at 3 km of depth and well corresponds to the simplified analytic models of a sliding planar surface resulting from GPS data inversions

Caratterizzazione sismica del sistema strutturale Pernicana - Provenzana (settore NE dell'Etna) attraverso l'utilizzo di differenti tecniche di rilocalizzazione.

Il fianco nord-orientale dell’Etna è interessato da un noto sistema strutturale denominato Pernicana-Provenzana, che ha un andamento WNW–ESE. Esso è collegato ad ovest ad un altro importante elemento strutturale, il Rift di Nord-Est, che mostra avere un ruolo importante nel controllo dei fenomeni di instabilità del fianco orientale del vulcano. La sismicità associata a questo sistema strutturale è di tipo superficiale (max 2-3 km b.s.l.) e rilevanti fenomeni di creeping sono rilevabili sul suo segmento orientale. I terremoti associati a questo sistema di faglie, che possono raggiungere magnitudo sino a 4.3, qualche volta con fenomeni di fagliazione superficiale, hanno provocato danni importanti alle principali strutture alberghiere ed ai paesi ubicati in prossimità della struttura. Nel presente lavoro, sono riportati i risultati di uno studio di dettaglio della sismicità localizzata lungo tale sistema strutturale, nel periodo 1999-2009. I terremoti registrati dalla rete sismica permanente dell’Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Catania, localizzati con un modello 1D utilizzando l’algoritmo Hypoellipse (Gruppo Analisi Dati Sismici, 2010), sono stati rilocalizzati applicando due differenti tecniche di localizzazione: NonLinLoc sviluppato da Lomax et al. (2000) e HypoDD proposto da Waldhauser & Ellsworth (2000). La prima metodologia è basata su un processo di ricerca globale, nello spazio 3D, dei parametri di localizzazione che possono essere ottenuti utilizzando diversi algoritmi. Il metodo HypoDD, che non prevede l’utilizzo di un modello 3D, è invece basato sull’algoritmo della doppia differenza che minimizza i residui tra le differenze dei traveltime osservati e calcolati per coppie di terremoti a stazioni comuni. L’applicazione di tali tecniche ha permesso di ottenere localizzazioni ipocentrali di migliore qualità, fondamentali per la caratterizzazione sismica della struttura. L’applicazione di queste differenti metodologie ha permesso di evidenziare che il sistema strutturale Pernicana- Provenzana risulta composto da segmenti caratterizzati da differenti rilasci di energia sismica. Sono stati individuati due cluster principali di terremoti, la cui distribuzione spaziale ha evidenziato un differente verso nell’immersione dei piani di faglia collegabili a questa sismicità. Infine, l’applicazione di tecniche di cross-correlazione delle forme d’onda registrate nel periodo indagato ha consentito di individuare “famiglie” di terremoti. L’analisi spazio – temporale delle famiglie individuate ha evidenziato per alcune di esse, una ricorrenza temporale ed ha permesso di ipotizzare che l’applicazione di un campo di stress sul sistema Pernicana-Provenzana potrebbe essere capace di attivare le stesse sorgenti sismiche in differenti periodi

PARTOS - Passive and Active Ray TOmography Software: description and preliminary analysis using TOMO-ETNA experiment’s dataset.

In this manuscript we present the new friendly seismic tomography software based on joint inversion of active and passive seismic sources called PARTOS (Passive Active Ray TOmography Software). This code has been developed on the base of two well-known widely used tomographic algorithms (LOTOS and ATOM-3D), providing a robust set of algorithms. The dataset used to set and test the program has been provided by TOMO-ETNA experiment. TOMO-ETNA database is a large, highquality dataset that includes active and passive seismic sources recorded during a period of 4 months in 2014. We performed a series of synthetic tests in order to estimate the resolution and robustness of the solutions. Real data inversion has been carried out using 3 different subsets: (i) active data; (ii) passive data; and (iii) joint dataset. Active database is composed by a total of 16,950 air-gun shots during 1 month and passive database includes 452 local and regional earthquakes recorded during 4 months. This large dataset provides a high ray density within the study region. The combination of active and passive seismic data, together with the high quality of the database, permits to obtain a new tomographic approach of the region under study never done before. An additional user-guide of PARTOS software is provided in order to facilitate the implementation for new users.PublishedS04351V. Storia e struttura dei sistemi vulcaniciJCR Journalope

Advances on the automatic estimation of the P-wave onset time.

This work describes the automatic picking of the P-phase arrivals of the 3*10^6 seismic registers originated during the TOMO-ETNA experiment. Air-gun shots produced by the vessel “Sarmiento de Gamboa” and contemporary passive seismicity occurring in the island are recorded by a dense network of stations deployed for the experiment. In such scenario, automatic processing is needed given: (i) the enormous amount of data, (ii) the low signal-to-noise ratio of many of the available registers and, (iii) the accuracy needed for the velocity tomography resulting from the experiment. A preliminary processing is performed with the records obtained from all stations. Raw data formats from the different types of stations are unified, eliminating defective records and reducing noise through filtering in the band of interest for the phase picking. The advanced multiband picking algorithm (AMPA) is then used to process the big database obtained and determine the travel times of the seismic phases. The approach of AMPA, based on frequency multiband denoising and enhancement of expected arrivals through optimum detectors, is detailed together with its calibration and quality assessment procedure. Examples of its usage for active and passive seismic events are presented.PublishedS04342V. Dinamiche di unrest e scenari pre-eruttiviJCR Journalope

Seismic Tomography Experiment at Italy's Stromboli Volcano

From 25 November to 2 December 2006, the first active seismic tomography experiment at Stromboli volcano was carried out with the cooperation of four Italian research institutions. Researchers on board the R/V Urania of the Italian National Council of Research (CNR), which was equipped with a battery of four 210- cubic- inch generated injection air guns (GI guns), fired more than 1500 offshore shots along profiles and rings around the volcano.DPC/INGV agreement 2004-2006Published269-2701.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani3.6. Fisica del vulcanismoN/A or not JCRreserve

Quantifying probabilities of eruption at a well-monitored active volcano: an application to Mount Etna (Sicily, Italy).

At active volcanoes, distinct eruptions are preceded by complex and different precursory patterns; in addition, there are precursory signals which do not necessarily lead to an eruption. The main purpose of this paper is to present an unprecedented application of the recently developed code named BET_EF (Bayesian Event Tree_Eruption Forecasting) to the quantitative estimate of the eruptive hazard at Mt. Etna volcano. We tested the model for the case history of the July-August 2001 flank eruption. Anomalies in geophysical, geochemical and volcanological monitoring parameters were observed more than a month in advance of the effective onset of the eruption. As a consequence, eruption probabilities larger than 90% were estimated. An important feature of the application of BET_EF to Mt. Etna was the probabilistic estimate of opening vent locations. The methodology allowed a clear identification of assumptions and monitoring parameter thresholds and provided rational means for their revision if new data or information are incoming