[1] The Southeast Crater of Mount Etna (Italy) was characterized by a violent eruptive activity between 26 January and 24 June 2000. This activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days. We estimated a volume of about 15-20 Â 10 6 m 3 lava and at least 2-3 Â 10 6 m 3 of tephra. We compared the paroxysmal volcanic activity to its associated seismic signature: The high number of events highlighted a strict correlation between tremor and volcanic activity. Seismic and volcanic characteristics, such as the frequency of occurrence, the duration of lava fountains and the associated tremor energy, suggested the subdivision of the studied period into two stages separated by the 20 February event. Combining volcanic with seismic data, we observed some useful relationships among lava fountain height, sustained column height and Reduced Displacement; in addition, we found that the entire episode was well correlated with the duration of the amplitude increase. Computing the tremor energy linked to each event, the total energy associated with lava fountains episodes results in 76% of the energy released during the whole period. Finally, the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode.

The Calabrian Arc subduction-rollback system along the convergent Africa/Eurasia plate boundary is among the most active geological structures in the Mediterranean Sea. However, its seismogenic behaviour is largely unknown, mostly due to the lack of seismological observations. We studied low-to-moderate magnitude earthquakes recorded by the seismic network onshore, integrated by data from a seafloor observatory (NEMO-SN1), to compute a lithospheric velocity model for the western Ionian Sea, and relocate seismic events along major tectonic structures. Spatial changes in the depth distribution of earthquakes highlight a major lithospheric boundary constituted by the Ionian Fault, which separates two sectors where thickness of the seismogenic layer varies over 40 km. This regional tectonic boundary represents the eastern limit of a domain characterized by thinner lithosphere, arc-orthogonal extension, and transtensional tectonic deformation. Occurrence of a few thrust-type earthquakes in the accretionary wedge may suggest a locked subduction interface in a complex tectonic setting, which involves the interplay between arc-orthogonal extension and plate convergence. We finally note that distribution of earthquakes and associated extensional deformation in the Messina Straits region could be explained by right-lateral displacement along the Ionian Fault. This observation could shed new light on proposed mechanisms for the 1908 Messina earthquake.

Volcanic eruptions may create a wide range of risks in inhabited areas and, as a consequence, major economic damage to the surrounding territory. An example of volcanic hazard was given between 1998 and 2001 by Mt. Etna volcano, in Italy, with its frequent paroxysmal explosive activity that caused more than a hundred fire-fountain episodes. In the period January-June 2000, in particular, 64 lava fountains took place at the Southeast Crater. During the most intense explosive phase of each episode, a sustained column often formed, reaching up to 6 km above the eruptive vent. Then, the column started to expand laterally causing more or less copious tephra fallout on the slopes of Etna; ash and lapilli, therefore, constituted a serious danger for vehicular and air traffic. A software and hardware warning system was developed to mitigate the volcanic hazard indicating the areas affected by potential ash and lapilli fallout. The alert system was mainly based on the good correspondence between the pattern of volcanic tremor amplitude and the evolution of explosive activity. When a fixed tremor threshold was exceeded, a semiautomatic process started to send faxes to Civil Defence and Municipalities directly affected by tephra fallout, together with information on wind directions from the Meteorological Office. The application of this methodology, during the last 14 eruptive episodes in 2000 and the 14 events occurred in 2001, demonstrated the good correspondence between the forecasts on the areas affected by tephra fallout and the effective tephra distribution on land. Despite the integrity of the performance provided by the alert system, small discrepancies occurred in the technical procedure of alerting, for which possible solutions have been discussed. The improvement of this type of system, could become basic for the Etnean region and be proposed for similar volcanic areas throughout the world.

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The spatial pattern of the b value of the frequency‐magnitude relation has been analyzed using gridding techniques beneath Mount Etna, Italy. A regional data set of 2900 events with Md (duration magnitude) ≥1.5 up to 15 km depth occurring between August 1999 and December 2005 has been used. Two regions with an abnormally high b value have been found, one centered beneath the southern part of the Valle del Bove, above the 6 km below sea level (bsl) deep basement, and the other beneath the summit region 2 km bsl east of the Central Craters. We can infer that these high b value anomalies are regions of increased crack density, and/or high pore pressure, related to the presence of nearby magma storage. This interpretation is supported by all the available geophysical evidence, such as tomographic studies and geodetic deformation measurements. The data set has also been subdivided into five periods, corresponding to different phases of volcanic activity: 2001 preeruption, 2001 eruptive, 2002–2003 preeruption, 2002–2003 eruptive, and 2002–2003 posteruption. The minimum magnitude of completeness, Mc, and the b value were computed for each period. A volume of anomalously high b values can be observed in each of these periods (except for the 2002–2003 preeruption interval). This approach has allowed the detection of the transient presence of magmatic intrusions during the various periods evaluated.