ALBERT

Description: SUMMARY Active volcanoes generate sonic and infrasonic signals, whose investigation provides useful information for both monitoring purposes and the study of the dynamics of explosive phenomena. At Mt. Etna volcano (Italy), a pattern recognition system based on infrasonic waveform features has been developed. First, by a parametric power spectrum method, the features describing and characterizing the infrasound events were extracted: peak frequency and quality factor. Then, together with the peak-to-peak amplitude, these features constituted a 3-D ‘feature space’; by Density-Based Spatial Clustering of Applications with Noise algorithm (DBSCAN) three clusters were recognized inside it. After the clustering process, by using a common location method (semblance method) and additional volcanological information concerning the intensity of the explosive activity, we were able to associate each cluster to a particular source vent and/or a kind of volcanic activity. Finally, for automatic event location, clusters were used to train a model based on Support Vector Machine, calculating optimal hyperplanes able to maximize the margins of separation among the clusters. After the training phase this system automatically allows recognizing the active vent with no location algorithm and by using only a single station.

Description: The 2001 Etna eruption occurred from July 17th to August 9th, 2001 and was preceded by several days of intense seismicity and ground deformation. We investigated the seismic activity recorded during November 2000 - June 2001 interval time preceding the eruption, to understand the meaning of the seismicity connected to the dike intrusion, that locally modified the stress field acting in the area. The earthquakes were recorded by the permanent local networks operating during that time and run by the Istituto Internazionale di Vulcanologia (IIV-CNR) and the Sistema POSEIDON. During the analyzed period, 683 earthquakes have been firstly localized by means of a 1D velocity model derived from Hirn et al., 1991 using the software HypoEllipse [Lahr, U. S. Geol. Survey, Open-File Report, 89/116, 81 pp., 1989]. In order to further improve the quality of the seismic dataset, we extracted 522 earthquakes with Gap less than 200°, Erh 〈 1.5 km, Erz 〈 2 km, RMS less than 0.5 sec, and a minimum number of S phases equal to 2. This latter seismic dataset was relocated using TomoDD code [Zhang and Thurber, BSSA, 93, 1875-1889. 2003] and a 3D velocity model [Patanè et al., Science, 313, 821- 823, 2006 after modified]. Using first motion polarity data, 3D fault plane solutions were computed by means of the software FPFIT [Reasenberg and Oppenheimer, U.S. Geological Survey Open File Report, 85/739, 109 pp, 1985]. Then, adopting restricted selection criteria (Npol more than 12; focal plane uncertainties less than 20°; number of solutions 〈 2; number of discrepancies less than 15%), we selected 116 FPSs. This dataset represented the input file for the stress and strain tensors computation using the inversion codes developed by Gephart and Forsyth,[ JGR 89: 9305-9320, 1984] and by Kostrov [Izv Acad Sci USSR Phys Solid Earth, 1, 23-40], respectively. On the basis of P and T axes distribution and the orientation of the main seismogenic stress and strain axes, we put some seismological constraints on the recharging phase leading to the 2001 Etna eruption.

Description: Published

Description: Salina

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: In 1966, the Istituto Internazionale di Vulcanologia (I.I.V.), gave the go ahead to the ambitious project of setting up a seismic network in the southern Tyrrhenian Sea, an area of extraordinary geophysical interest, which until then was not covered by seismic monitoring. At the time, there were single seismic stations on the rest of the italian peninsula. These were inside universities, public and private bodies and at the numerous observatories of the Istituto Nazionale di Geofisica (founded in 1936 by Antonino Lo Surdo and becoming independent of the Consiglio Nazionale delle Ricerche (C.N.R,. in 1945) and still used mechanical seismographs, with masses weighing from 80 up to 1300 Kg. On the Aeolian Islands instead, electromagnetic seismometers were employed from the start. The experimental network, planned in the Willmore laboratories at Edinburgh and tested in the Aeolian Islands over a two-year period, represented the starting point for the Permanent Seismic Network (PSN) of the Southern Tyrrhenian. After the experience of the Laboratorio Internazionale per le Ricerche Vulcanologiche (L.I.R.V. - C.N.R.), of the Istituto di Vulcanologia of the University of Catania, the independent I.I.V. - C.N.R., together with the observatory, was launched in 1969. In the course of the seventies, every island of the Aeolian archipelago, was equipped with at least a seismic station and the 3 sensor systems (triaxial systems) began to become widely used. In the eighties, the “Sismologia Eolie” project was started, aimed at a further develop and update the seismic net. With the wide use of magnetic tape recording, the instrumental data stored could be more readily transported on suitable drums to the main centre in Catania for analysis. Here, Research Units were established in order to prepare the way for enhanced interaction between technical staff and research groups. The instrumental geophysical investigations, progressively extended and in a permanente form to Eastern Sicily and particular around Etna. From the nineties, operations room in Catania was fully active, working 24/24, and ensuring the seismic and volcanic surveillance of Etna, Stromboli and Vulcano. The Geophysical Observatory of Lipari and the main centre of the Institute in Catania, were merged in 2001 into the new Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the network of the Aeolian Islands became an integral part of the Permanent Seismic Network (PSN) of Eastern Sicily and Southern Calabria. Special prominence will be given in the course of this historical reconstruction to the evolution of instrumental seismology, thanks to forty years of continuous input, indispensable for the understanding of the seismogenetic processes in the area, this still represents the chief undertaking of the geophysical observatory on Lipari, whose important scientific but also social role must be acknowledged in the growing interaction between research and civil protection.

Description: Published

Description: 1-40

Description: 1.1. TTC - Monitoraggio sismico del territorio nazionale

Description: N/A or not JCR

Description: open