Publication Date:
2017-04-04
Description:
Mt. Etna lies in front of the southeast-verging Apennine-Maghrebian fold-and-thrust belt,
where the NNW-trending Malta Escarpment separates the Sicilian continental crust from the
Ionian Mesozoic oceanic basin, presently subducting beneath the Calabrian arc (Selvaggi
and Chiarabba, 1995). Seismic tomographic studies indicate the presence of a mantle plume
beneath the volcano with a Moho transition at depth less than 20 km (Nicolich et al.,2000;
Barberi et al., 2006). Geophysical and geological evidences suggest that the Mt. Etna magma
ascent mechanism is related to the major NNW-trending lithospheric fault (Doglioni et al.,
2001). However, the reason for the Mt. Etna mantle plume draining and channeling the
magma from the upper mantle source to the surface is not yet clear. All models proposed in
literature (Rittmann, 1973; Tanguy et al., 1997; Monaco et al.; 1997; Gvirtzman and Nur,
1999; Doglioni et al., 2001) do not explain why such a mantle plume has originated in this
anomalous external position with respect to the arc magmatism and back-arc spreading
zones associated with the Apennines subduction. Some ideas on the subduction rollback
must be better developed through the comparison with new regional tomographic studies
that are being released. Moreover, tomographic studies reveal a complex and large
plumbing system below the volcano from -2 to -7 km a.s.l., wide up to 60 km2 that reduces
itself in size down to -18 km of depth close to the apex of the mantle plume. Chiocci et al.
(2011) found a large bulge on the underwater continental margin facing Mt. Etna, and
suggested that the huge crystallized magma body intruded in the middle and upper
continental crust was able to trigger an instability process involving the Sicilian continental
margin during the last 0.1 Ma. This phenomenon induces the sliding of the volcano eastern
flank observed since the 90s (Borgia et al, 1992; Lo Giudice and Rasà, 1992) because the
effects of the bulge collapse are propagating upslope, and the continuous decompression at
the volcano summit favors the ascent of basic magma without lengthy storage in the upper
crust, as one might expect in a compressive tectonic regime. Taken together, these new
evidences (tomographic, tectonic, volcanic) are concerned with the exceptional nature of Mt.
Etna and raise the need to explain the origin of the mantle plume that supplies its
volcanism. The lower crust and the uppermost mantle need to be better resolved in future
experiments and studies. The use of regional and teleseismic events for tomography and
receiver function analyses is required to explore a volume that has only marginally been
investigated to date. The relation between the magma source in the mantle and the upper
parts of the system, as well as the hypothesis above reported on the relation between
tectonics and volcanism and the role of lithospheric faults, could be resolved only by
applying seismological techniques able to better constrain broader and deeper models.
Finally, although the recent tomographic inversions have progressively improved our
knowledge of Etna’s shallow structure, highlighting a complex pattern of magma chambers
and conduits with variable dimensions, the geometry of the conduits and the dimensions
and shapes of small magmatic bodies still require greater investigation. Their precise
definition is crucial to delineate a working model of this volcano in order to understand its
behaviour and evolution. For this purpose, at least within the volcanic edifice, the precise
locations of the seismo-volcanic signals can be considered a useful tool to constrain both the
area and the depth range of magma degassing and the geometry of the shallow conduits. In
this work, we furnish evidences that the tremor and LP locations allowed to track magma
migration during the initial phase of the 2008-2009 eruption and in particular the initial
northward dike intrusion, also confirmed by other geophysical, structural and volcanological observations (Aloisi et al., 2009; Bonaccorso et al., 2011), and the following
fissure opening east of the summit area at the base of SEC. All these evidences, obtained by
the marked improvement in the monitoring system together with the development of new
processing techniques, allowed us to constrain both the area and the depth range of magma
degassing, highlighting the geometry of the magmatic system feeding the 2008-2009
eruption.
Description:
Published
Description:
73-104
Description:
1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
Description:
open
Keywords:
Volcano seismology
;
Etna
;
tectonics
;
volcanic tremor
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
book chapter
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