19 research outputs found
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
TOMO-ETNA experiment at Etna volcano: Activities on land
In the present paper we describe the on-land field operations integrated in
the TOMO-ETNA experiment carried out in June-November 2014 at Mt.
Etna volcano and surrounding areas. This terrestrial campaign consists
in the deployment of 90 short-period portable three-component seismic
stations, 17 broadband seismometers and the coordination with 133 permanent
seismic station belonging to Italy’s Istituto Nazionale di Geofisica
e Vulcanologia (INGV). This temporary seismic network recorded active
and passive seismic sources. Active seismic sources were generated
by an array of air-guns mounted in the Spanish oceanographic vessel
“Sarmiento de Gamboa” with a power capacity of up to 5200 cubic
inches. In total more than 26,000 shots were fired and more than 450 local
and regional earthquakes were recorded. We describe the whole technical
procedure followed to guarantee the success of this complex seismic experiment.
We started with the description of the location of the potential
safety places to deploy the portable network and the products derived from
this search (a large document including full characterization of the sites,
owners and indication of how to arrive to them). A full technical description
of the seismometers and seismic sources is presented. We show
how the portable seismic network was deployed, maintained and recovered
in different stages. The large international collaboration of this experiment
is reflected in the participation of more than 75 researchers,
technicians and students from different institutions and countries in the
on-land activities. The main objectives of the experiment were achieved
with great success.PublishedS04272SR. VULCANI - Servizi e ricerca per la SocietàJCR Journalope
Characterization of seismicity at Mt. Etna volcano (Italy) by inter-event time distribution
The space time inter-event time (IET) distributions of earthquakes occurring from 1988 to 2011 at Mt. Etna are
analysed in order to identify the periodicity or stationary behaviour of seismicity, and to correlate it with the
volcano-tectonic features of the region. The comparison between IET distributions at Etna with those obtained
both for Sicily and Italy, shows that IETs at a larger scale are well-modelled by a gamma distribution, whereas
at Etna local scale they are characterised by a bimodal curve, in which the two peaks are related to: (i) the contribution of local seismic swarms with very short inter-event times, and (ii) the background regional stationary
seismicity. IET analysis is an important tool to investigate the behaviour of seismicity at different crustal levels in the Etna region, distinguishing sectors that are influenced by volcano dynamics or regional tectonics. Indeed, the spatial
variation of IET distributions, obtained by analysing different Etna crustal sectors, shows that seismicity shallower
than 5 km is almost entirely characterised by short inter-event times and is mainly confined to the summit area.
For earthquakes deeper than 5 km occurring in the eastern flank of the volcano, as well as in eastern Sicily, IET
distributions are characterised by independent events which suggest that both areas are influenced by the
same extensional regional regime. By contrast, IET distributions obtained for the western flank and northwestern
Sicily are marked by two peaks, indicating that the compressional stress is acting in both areas
Characterization of seismicity at Mt. Etna volcano (Italy) by inter-event time distribution
The space time inter-event time (IET) distributions of earthquakes occurring from 1988 to 2011 at Mt. Etna are
analysed in order to identify the periodicity or stationary behaviour of seismicity, and to correlate it with the
volcano-tectonic features of the region. The comparison between IET distributions at Etna with those obtained
both for Sicily and Italy, shows that IETs at a larger scale are well-modelled by a gamma distribution, whereas
at Etna local scale they are characterised by a bimodal curve, in which the two peaks are related to: (i) the contribution of local seismic swarms with very short inter-event times, and (ii) the background regional stationary
seismicity. IET analysis is an important tool to investigate the behaviour of seismicity at different crustal levels in the Etna region, distinguishing sectors that are influenced by volcano dynamics or regional tectonics. Indeed, the spatial
variation of IET distributions, obtained by analysing different Etna crustal sectors, shows that seismicity shallower
than 5 km is almost entirely characterised by short inter-event times and is mainly confined to the summit area.
For earthquakes deeper than 5 km occurring in the eastern flank of the volcano, as well as in eastern Sicily, IET
distributions are characterised by independent events which suggest that both areas are influenced by the
same extensional regional regime. By contrast, IET distributions obtained for the western flank and northwestern
Sicily are marked by two peaks, indicating that the compressional stress is acting in both areas.Published1-92V. Dinamiche di unrest e scenari pre-eruttiviJCR Journalrestricte
Volcanic unrest leading to the July-August 2001 lateral eruption at Mt. Etna: seismological constraints
A close relationship between earthquake swarms, volcanic eruptions, and ground deformation at Mt. Etna was
well documented shortly before the beginning of the July–August 2001 eruption. Past experiences at this volcano
suggest how magma/dike intrusion in the shallow crust or in the upper part of the volcanic pile normally occurs
after several years/months of internal recharging. Since seismic investigations provide a means to study the scale
and origin of stress perturbations at active volcanoes, allowing to better investigating the preparation phase of an
eruption, in this paper, we performed a close examination of the seismic activity recorded at Mt. Etna in the
months preceding the 2001 eruption and in particular between November 2000 and July 2001. After integrating
data recorded by the two networks operating during that time and run by the Istituto Internazionale di
Vulcanologia and SISTEMA POSEIDON, we relocated 522 earthquakes by using the tomoDD code in a 3D velocity
model, and then we computed their fault plane solutions. The application of different selection criteria enabled
obtaining a good-quality revised data set consisting of 111 fault plane solutions.
The high-precision locations identified well-defined seismic clusters, in different periods, suggesting a link with
the magma migration from a depth of 8–13 km b.s.l. towards shallower zones. Moreover, the computed maximum
compressive stress axis, as inferred from earthquake focal mechanisms, indicated a roughlyW-E-oriented
σ1. This findings reflect an overpressure of the mid to shallow crust due to the progressive magma uprising in
central portion of the volcano and also highlighted a rotation of the local stress field with respect to the regional
one N-S trending. In addition, P-axis distribution pointed out the presence of a center of pressure located to the
south of the Central Craters.
These results provide particularly compelling evidence for a direct causal link between pressurization of the midlevel
volcanic plumbing system by ascending magma and precursory local stress field reorientations, demonstrating
that seismological analysis can be used to detect subtle local stress changes that herald eruptive activity
Seismological constraints on the intrusive mechanism leading the 2001 Etna eruption
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.PublishedSalina1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attiveope
Volcanic unrest leading to the July-August 2001 lateral eruption at Mt. Etna: seismological constraints
A close relationship between earthquake swarms, volcanic eruptions, and ground deformation at Mt. Etna was
well documented shortly before the beginning of the July–August 2001 eruption. Past experiences at this volcano
suggest how magma/dike intrusion in the shallow crust or in the upper part of the volcanic pile normally occurs
after several years/months of internal recharging. Since seismic investigations provide a means to study the scale
and origin of stress perturbations at active volcanoes, allowing to better investigating the preparation phase of an
eruption, in this paper, we performed a close examination of the seismic activity recorded at Mt. Etna in the
months preceding the 2001 eruption and in particular between November 2000 and July 2001. After integrating
data recorded by the two networks operating during that time and run by the Istituto Internazionale di
Vulcanologia and SISTEMA POSEIDON, we relocated 522 earthquakes by using the tomoDD code in a 3D velocity
model, and then we computed their fault plane solutions. The application of different selection criteria enabled
obtaining a good-quality revised data set consisting of 111 fault plane solutions.
The high-precision locations identified well-defined seismic clusters, in different periods, suggesting a link with
the magma migration from a depth of 8–13 km b.s.l. towards shallower zones. Moreover, the computed maximum
compressive stress axis, as inferred from earthquake focal mechanisms, indicated a roughlyW-E-oriented
σ1. This findings reflect an overpressure of the mid to shallow crust due to the progressive magma uprising in
central portion of the volcano and also highlighted a rotation of the local stress field with respect to the regional
one N-S trending. In addition, P-axis distribution pointed out the presence of a center of pressure located to the
south of the Central Craters.
These results provide particularly compelling evidence for a direct causal link between pressurization of the midlevel
volcanic plumbing system by ascending magma and precursory local stress field reorientations, demonstrating
that seismological analysis can be used to detect subtle local stress changes that herald eruptive activity.Published11-231T. Geodinamica e interno della TerraJCR Journalrestricte
Volcanic unrest leading to the July-August 2001 lateral eruption at Mt. Etna: seismological constraints
A close relationship between earthquake swarms, volcanic eruptions, and ground deformation at Mt. Etna was
well documented shortly before the beginning of the July–August 2001 eruption. Past experiences at this volcano
suggest how magma/dike intrusion in the shallow crust or in the upper part of the volcanic pile normally occurs
after several years/months of internal recharging. Since seismic investigations provide a means to study the scale
and origin of stress perturbations at active volcanoes, allowing to better investigating the preparation phase of an
eruption, in this paper, we performed a close examination of the seismic activity recorded at Mt. Etna in the
months preceding the 2001 eruption and in particular between November 2000 and July 2001. After integrating
data recorded by the two networks operating during that time and run by the Istituto Internazionale di
Vulcanologia and SISTEMA POSEIDON, we relocated 522 earthquakes by using the tomoDD code in a 3D velocity
model, and then we computed their fault plane solutions. The application of different selection criteria enabled
obtaining a good-quality revised data set consisting of 111 fault plane solutions.
The high-precision locations identified well-defined seismic clusters, in different periods, suggesting a link with
the magma migration from a depth of 8–13 km b.s.l. towards shallower zones. Moreover, the computed maximum
compressive stress axis, as inferred from earthquake focal mechanisms, indicated a roughlyW-E-oriented
σ1. This findings reflect an overpressure of the mid to shallow crust due to the progressive magma uprising in
central portion of the volcano and also highlighted a rotation of the local stress field with respect to the regional
one N-S trending. In addition, P-axis distribution pointed out the presence of a center of pressure located to the
south of the Central Craters.
These results provide particularly compelling evidence for a direct causal link between pressurization of the midlevel
volcanic plumbing system by ascending magma and precursory local stress field reorientations, demonstrating
that seismological analysis can be used to detect subtle local stress changes that herald eruptive activity
The borehole dilatometers network of Mt. Etna : a powerful tool to detect and infer volcano dynamics
A network of four borehole dilatometers has been installed on Etna in two successive phases (2010–2011 and 2014). The borehole dilatometers are installed in holes drilled at depths usually greater than 100 m, and they measure the volumetric strain of the surrounding rock with a nominal precision up to 10^-11 in a wide frequency range (10^-7–25 Hz). Here we describe the characteristics of the network and the results of the in situ calibrations obtained after the installations by different methods. We illustrate short-term strain changes recorded during several lava fountains erupted by Etna during 2011–2013, and we also show signal changes recorded at all four stations during the lava fountain on 28 December 2014. Analytical and numerical computations constrained the eruptions source depth and also its volume change that is related to the magma volume emitted. Finally, we show the potential of the signal in the medium term to reveal strain changes related to different phases of the volcanic activity.Published4655–46691IT. Reti di monitoraggio e OsservazioniJCR Journalrestricte
Seismological constraints on the intrusive mechanism leading the 2001 Etna eruption
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