S. Gambino

Il 9 gennaio 2001 uno sciame sismico localizzato sul fianco sud-orientale dell'Etna e caratterizzato da forme d'onda molto simili, ha prodotto diversi danni all'abitato di Zafferana Etnea, che dista circa 3 km dall'area epicentrale. Un'analisi della sismicità registrata a partire dal 1994, ha rivelato che altri terremoti con le stesse caratteristiche hanno interessato quest'area; alcuni hanno preceduto o seguito per alcuni mesi lo sciame del gennaio 2001, altri sono stati registrati ben cinque anni prima. L'utilizzo di tecniche di cross-correlazione, applicato su 3 famiglie di eventi, ha permesso di ottenere una precisa distribuzione spaziale degli ipocentri (errore medio 10-20 metri) e conseguentemente di descrivere la geometria di faglia. La direzione di tale discontinuità, coincidente con uno dei piani nodali ottenuti dai meccanismi focali (che prevede movimenti di tipo strike destro), risulta coerente con uno dei principali trend regionali che interes...

ABSTRACT On 9 of January 2001 the INGV seismic network of Catania (Italy) recorded a seismic swarm of about 60 earthquakes with 1.0>Md>3.6, and nearly identical seismograms. The main shock caused damage to the town of Zafferana Etnea 2.5 km distant from the epicenter located on SE flank of the volcano. Some other events with similar waveform forecasted (up to 2 months before) and followed (for about one month) this swarm; moreover a check of Mt. Etna SE flank seismicity, starting from 1994, has permitted to identify a cluster of 6 multiplets recorded on August 1995 whose seismograms are strongly coherent with the January 9, 2001 ones. Thus we recognize for the first time the occurrence of seismic events on Mount Etna with nearly identical sources separated by years. We applied a cross-spectral technique that allows to obtain the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques. The results describe clearly the geometry of the seismogenetic structure; the events lie on planes oriented ENE-WSW that are coincident with one of the planes of the focal mechanism obtained by first-arrivals polarities. This alignment is coherent with one of the main regional tectonic trends that characterize the Mt. Etna area The multiplets analysis has allowed to recognize, on SE flank, a right-lateral strike seismic source along ENE-WSW fault plane, 4 km deep, time repeated and able to produce strong releases.

On October 27, 2002, after about 15 months of quiescence Mt. Etna started a new eruption, still in progress, that has involved the forming of eruptive fracture both on south and north flanks of the volcano. A permanent tilt network that comprises nine bi-axial instruments installed in shallow boreholes and a mercury long-base guarantees continuous tilt measurements on Mt. Etna

... Page 6. 310 Salvatore Gambino and Eugenio Privitera PAGEOPH, ... 5, Table 2). Simple ground components ratio (JURKEVICS, 1988; SUTEAU-HENSON, 1991; RIVIERE-BARBIER et al., 1992) furnishes useful data to differentiate Swaves from surface waves. ...

The multi-parametric permanent system (tilt and GPS networks, robotized geodetic station) for monitoring ground deformation at Stromboli volcano was set up in the 1990s and later greatly improved during the effusive event of 2002–2003. Unlike other volcanoes, e.g. Mt. Etna, the magnitude of ground deformation signals of Stromboli is very small and through the entire period of operation of the

ABSTRACT Ground deformations measured during the last two GPS surveys carried out in March 2006 and September 2007 on the Lipari-Vulcano network are analyzed. Through this period, the monitoring seismic network measured an increase of seismic strain release around the Lipari-Vulcano complex with respect to the previous years. GPS surveys measured a significant N-ward motion of Vulcano island with respect to the ITRF05. This motion abruptly decreases in the N part of Vulcano, suggesting a decoupling of the main Vulcano island from the rest of the volcanic complex. By assuming a local reference frame, we observed that the Lipari island and the northernmost part of the Vulcano island are moving SSE-ward with respect to the central and southernmost part of the Vulcano island. GPS data also highlighted a local uplift of the ``La Fossa'' cone superimposed on the general subsidence of the island, increasing towards N. The vertical movements measured by GPS are compared with the results of the leveling surveys carried out on the network installed and managed by the INGV - Osservatorio Vesuviano for monitoring vertical ground movements on Volcano island. Height variations are computed with respect to a reference benchmark located on the southern part of the island, which is a relatively stable area compared to the northern part. The comparison between the two most recent surveys (October 2003 and October 2008) indicates a significant subsidence of the centre-northern area of the island (bottom Fossa Crater and Vulcanello). We also analyzed the long-term tilt observations through the same period. The tilt network at Vulcano Island currently has five borehole stations, four of which are installed at depth of 8-10 m, allowing recording stable and highly accurate signals with low noise. Tilt vectors concur well with leveling and GPS data, highlighting a deflection towards the central-northern part of the island. Geodetic strain tensor analysis derived by GPS data was performed over the area covered by the Lipari-Vulcano network. Transpressive kinematics of the Lipari-Vulcano volcanic complex, with a main N-S contraction and a minor E-W extension only on the Southern part of Vulcano is revealed. In addition, data inversion was performed using a simple Okada model, inverting the horizontal strain measured on 258 GPS baselines. We prefer using baselines rather than displacement vectors to avoid bias due to the ambiguity in fixing the reference system. The final structural framework defines a main compression with a dextral component of displacement on a NW-SE striking structure. This kinematics agrees with focal mechanisms of the strongest seismic events recorded in this area over the same time span as the GPS surveys. Furthermore, a preliminary analysis shows that the observed tilt fits well with the expected one from the model.

The island of Vulcano is a composite volcanic edifice located in the south-central sector of the Aeolian Archipelago (Tyrrhenian Sea, Italy). The island, together with Lipari and Salina islands (fig. 1), represents the emerged part of the Tin-dari-Letojanni system (TL), a NW-SE ...

We investigated the relationship between volcano-seismic events, recorded at La Fossa crater of Vulcano (Aeolian Islands, Italy) during 2004-2006, and the dynamics of the hydrothermal system. During the period of study, three episodes of increasing numbers of volcano-seismic events took place at the same time as geothermal and geochemical anomalies were observed. These geothermal and geochemical anomalies have been interpreted

Mount Melbourne (74821? S, 164843? E) is a quiescent volcano located in 20 northern Victoria Land, Antarctica. Tilt signals have been recorded on Mount Melbourne since early 1989 by a permanent shallow borehole tiltmeter network comprising five stations. An overall picture of tilt, air and permafrost temperatures over 15 years of continuous recording data is reported. We focused our observations on long-term tilt trends that at the end of 1997 25 showed coherent changes at the three highest altitude stations, suggesting the presence of a ground deformation source whose effects are restricted to the summit area of Mount Melbourne. We inverted these data using a finite spherical body source, thereby obtaining a shallow deflation volume source located under the summit area. The ground deformation observed corroborates 30 the hypothesis that the volcanic edifice of Mount Melbourne is active and should be monitored multidisciplinarily. 35

On the 9 th of January 2001 a seismic swarm on the southeastern flank of Mt. Etna at 3.5 km beside sea level (b.s.l.), caused co-seismic variations on short and long baseline tiltmeters of the Mt. Etna permanent tilt network. Taking account of the geometry and mechanism of the active tectonic structure obtained by seismological studies, the theoretical tilt linked to the faulting source was calculated at multiple different recording stations. It was found that the amount of measured deformation exceeded that which was generated seismically, indicating that much of the deformation along the fault was aseismic. The 9 January 2001 episode represents a shear response to a local stress caused by a volcanic source that acted in the period preceding the 2001 eruption. Tilt data also suggest a marked slip of 70-140 cm along the fault, probably due to the presence of fluids.

The Timpe Fault System is the source of very shallow but destructive earthquakes that affect several towns and villages on the eastern flank of Mt. Etna (Italy). In 1984, several seismic events, and specifically on 19 and 25 October, caused one fatality, 12 injuries and produced serious damage in the Zafferana and Acireale territories. This seismicity was mainly related to the activity of the Fiandaca Fault, one of the structures belonging to the Timpe Fault System. We inverted ground deformation data collected by a geodimeter trilateration network set up in 1977 at a low altitude along the eastern side of the volcano in order to define the Timpe Fault System faulting mechanisms linked to the seismicity in 1984. We have found that in the period May 1980–October 1984, the Fiandaca Fault was affected by a strike-slip and normal dip-slip of about 20.4 and 12.7 cm respectively. This result is kinematically consistent with field observations of the coseismic ground ruptures along the fault but it is notably large compared to displacements estimated by seismic-ity, then suggesting that most of the slip over the fault plane was aseismic. The results once again confirm how seismicity and its relation with ground ruptures and creep displacement represent a very high hazard to the several towns and villages situated along the Timpe Fault System.

In July 2001, Mt. Etna experienced a pronounced increase in seismic activity heralding one of the most intense eruptions of the past 30 years which started on July 17. Between July 12 and 17, thousands of earthquakes were recorded by a dense seismic network run by the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania. Marked ground deformation was

ABSTRACT On October 27, 2002, after about 15 months of quiescence a new eruption, which is still in progress, started at Mt. Etna Volcano. In this work we considered the seismicity occurred between the end of the July-August 2001 and the beginning of the 2002 eruption recorded by the INGV-CT (Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania) seismic network. To obtain more precise hypocenter locations of ca 430 seismic events recorded in this period we applied the double-difference technique (HypoDD code) on the previously locations selected from the catalog database. For the relocation we used both 1D and 3D velocity models and we discuss the results and associated errors. These analyses have allowed to obtain a spatial distribution of the earthquakes with a higher precision with respect to the traditional localization techniques highlighting several clusters of events. In particular a group of earthquakes occurred between July and September 2002, located under the southern fissures area is well distributed along a narrow band striking in NNW direction with almost vertical dip and depth ranging between 8 and 18 km. Finally we also discuss computed focal solutions and spectral parameters for the more energetic events.

Several authors investigated the seismic behavior before Mt. Etna eruptions and some models were proposed in order to explain peculiar features of seismicity preceding flank eruptions. In particular, stress and strain fields seemed to modify their orienta- tion due to the action of magma overpressure. Recently, about 40 additional seismic stations boosted the Mt. Etna permanent network and enabled us

Riassunto. Nell'agosto 1999 ha avuto inizio la gestione scientifica del Sistema Poseidon che ha tra i suoi scopi principali quello di assicurare la sorveglianza e l'analisi della sismicità della Sicilia orientale. Nell'area etnea tale sorveglianza è garantita da una rete sismica permanente composta da 39 stazioni analogiche a corto periodo (1s), che rispetto a reti con maglia più larga che

About 1000 microearthquakes, occurring from January 2004 to December 2006 at La Fossa crater of Vulcano (Aeolian Islands, Italy) and related to processes of the geothermal system, have been analysed. Three episodes of increasing number of these seismic events, that accompanied geothermal and geochemical anomalies, took place during the studied time span. Six classes of microearthquakes (monochromatic, low frequency, medium frequency, high frequency, mixed, tornillos events), characterised by different spectral content and various similarity of the waveforms, have been recognized. We noted that events belonging to each class were not uniformly time distributed. In particular, the occurrence rate of microearthquakes of some classes seems to be more related to geothermal and geochemical anomalies than others. The microearthquakes, mainly clustered below La Fossa crater area at depth 0.5-1.1 km b.s.l., were space-distributed according to the classes. We infer that microseismicity at Vul...