Volcanic Tremor at Mt. Etna, Italy, Preceding and Accompanying the Eruption of July – August, 2001

Falsaperla, S.; Alparone, Salvatore; D’Amico, S.; Grazia, Giuseppe Di; Ferrari, F.; Langer, H.; Sgroi, Tiziana; Spampinato, S.

doi:10.1007/s00024-005-2710-y

Cited by 32 publications

(35 citation statements)

References 26 publications

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“…Changes in time and space of background seismic noise related to the volcanic activity are well documented. Falsaperla et al [2005] showed remarkable variation in amplitude and frequency content of the tremor of Mount Etna at seismic stations surrounding the summit crater area before and during the volcanic activity of July -August 2001. During the 2001 flank eruption they observed high tremor amplitude and a shift of the predominant frequencies toward frequencies (about 2 Hz) lower than those of the preeffusive phase.…”

Section: Introductionmentioning

confidence: 99%

Evidences for strong directional resonances in intensely deformed zones of the Pernicana fault, Mount Etna, Italy

et al. 2009

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[1] In this paper we investigate ground motion properties in the western part of the Pernicana fault. This is the major fault of Mount Etna and drives the dynamic evolution of the area. In a previous work, Rigano et al. (2008) showed that a significant horizontal polarization characterizes ground motion in fault zones of Mount Etna, both during earthquakes and ambient vibrations. We have performed denser microtremor measurements in the NE rift segment and in intensely deformed zones of the Pernicana fault at Piano Pernicana. This study includes mapping of azimuth-dependent horizontalto-vertical spectral ratios along and across the fault, frequency-wave number techniques applied to array data to investigate the nature of ambient vibrations, and polarization analysis through the conventional covariance matrix method. Our results indicate that microtremors are likely composed of volcanic tremor. Spectral ratios show strong directional resonances of horizontal components around 1 Hz when measurements enter the most damaged part of the fault zone. Their polarization directions show an abrupt change, by 20°to 40°, at close measurements between the northern and southern part of the fault zone. Recordings of local earthquakes at one site in the fault zone confirm the occurrence of polarization with the same angle found using volcanic tremor. We have also found that the directional effect is not time-dependent, at least at a seasonal scale. This observation and the similar behavior of volcanic tremors and earthquake-induced ground motions suggest that horizontal polarization is the effect of local fault properties. However, the 1-Hz resonant frequency cannot be reproduced using the 1-D vertically varying model inferred from the array data analysis, suggesting a role of lateral variations of the fault zone. Although the actual cause of polarization is unknown, a role of stress-induced anisotropy and microfracture orientation in the near-surface lavas of the Pernicana fault can be hypothesized consistently with the sharp rotation of the polarization angle within the damaged fault zone.

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Section: Introductionmentioning

confidence: 99%

Evidences for strong directional resonances in intensely deformed zones of the Pernicana fault, Mount Etna, Italy

et al. 2009

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“…1 and 2 Hz. During the episodes of FON the signal reached high energy as well, but the spectrum had a broader shape (see also Falsaperla et al 2005). During the PRE stage, spectrograms with yellow to light green tones in the frequency band below 5 Hz, and light blue colours above 5 Hz were typical, due to the lower levels of the seismic energy radiation.…”

Section: Seismic Datamentioning

confidence: 95%

“…2). The strict relationship between eruptive phenomena and volcanic tremor changes was described by Falsaperla et al (2005) and also documented by Alparone et al (2003), who, in particular, analysed high amplitudes of volcanic tremor during vigorous magma jets throughout repeated episodes of lava fountains in 2000. Moving on from these findings, we explored the possibility to reconstruct the Behncke & Neri (2003b).…”

Section: Eruptive Dynamics At Mt Etnamentioning

confidence: 95%

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Synopsis of supervised and unsupervised pattern classification techniques applied to volcanic tremor data at Mt Etna, Italy

Langer

Falsaperla

Masotti

et al. 2009

Geophysical Journal International

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SUMMARY States of volcanic activity at Mt Etna develop in well‐defined regimes with variable duration from a few hours to several months. Changes in the regimes are usually concurrent with variations of the characteristics of volcanic tremor, which is continuously recorded as background seismic radiation. This strict relationship is useful for monitoring volcanic activity in any moment and in whatever condition. We investigated the development of tremor features and its relation to regimes of volcanic activity applying pattern classification techniques. We present results from supervised and unsupervised classification methods applied to 425 patterns of volcanic tremor recorded between 2001 July and August, when a volcano unrest occurred. Support Vector Machine (SVM) and multilayer perceptron (MLP) were used as pattern classifiers with supervised learning. For the SVM and MLP training, we considered four target classes, that is, pre‐eruptive, lava fountains, eruptive and post‐eruptive. Using a leave one out testing scheme, SVM reached a score of 94.8 per cent of patterns matching the actual class membership, whereas MLP achieved 81.9 per cent of matching patterns. The excellent results, in particular those obtained with SVM, confirmed the reproducibility of the a priori classification. Unsupervised classification was carried out using cluster analysis (CA) and self‐organizing maps (SOM). The clusters identified in unsupervised classification formed well‐defined regimes, which can be easily related to the four a priori classes aforementioned. Besides, CA found a further cluster concurrent with the climax of eruptive activity. Applying a proper colour‐coding to the microclusters (the so‐called best matching units) identified by SOM, it was visually possible to follow the development of the characteristics of the tremor data with time, highlighting transitional stages from a regime of volcanic activity to another one. We conclude that supervised and unsupervised classification methods can be conveniently implemented as complementary tools for an in‐depth understanding of the relationships between tremor data and volcanic phenomena.

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“…The good correspondence between increases of tremor amplitude and summit explosive eruptions (Falsaperla et al 1994(Falsaperla et al , 2005 permitted a retrospective statistical ''forecast'' of lava fountain episodes for the 1989 eruption (Privitera et al 2003) and 1998-99 sequence (Alparone and Privitera 2001). Finally, detailed seismic tremor studies allowed a better characterization of the different eruptive phases occurring during the 2000 lava fountain episodes (Alparone et al 2003).…”

Section: Volcanic Tremormentioning

confidence: 98%

Alert system to mitigate tephra fallout hazards at Mt. Etna Volcano, Italy

et al. 2007

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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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Volcanic Tremor at Mt. Etna, Italy, Preceding and Accompanying the Eruption of July – August, 2001

Cited by 32 publications

References 26 publications

Evidences for strong directional resonances in intensely deformed zones of the Pernicana fault, Mount Etna, Italy

Evidences for strong directional resonances in intensely deformed zones of the Pernicana fault, Mount Etna, Italy

Synopsis of supervised and unsupervised pattern classification techniques applied to volcanic tremor data at Mt Etna, Italy

Alert system to mitigate tephra fallout hazards at Mt. Etna Volcano, Italy

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