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Marco Neri, Valerio Acocella and
Boris Behncke (2003)
Large-scale spreading of the eastern flank of
Mt. Etna (Italy)
during the 2002-2003 eruption
Abstract
presented at the EGS-AGU-EUG Joint Assembly, Nice, France, Geophysical
Research Abstracts, Vol. 5, 03636
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Mt. Etna is characterized
by active spreading of its eastern and southern flanks. The eastern
unstable area is bordered, to the north, by the E-W trending Pernicana
Fault System (PFS), previously believed to be ~9 km long. Its precise
eastern termination, and thus the extent of the collapsing area, were
not clearly defined, due to the lack of recent deformations and to the
presence of the sea. The surface fracturing associated with the 2002-2003
eruption permitted to properly evaluate the extent of the PFS and thus
of the spreading area. The fracture pattern along the PFS migrated in
fact from the NE Rift eastward to the coastline, nearly 20 km distant.
The deformation consisted of dextral en-echelon segments, with left-lateral
and normal kinematics. Both the left-lateral and the normal components
of displacement where 1 order of magnitude higher on the western portion
of the PFS. Nevertheless, the newly discovered eastern portion (~10
km long) is located in correspondence with previously displaced and
repaired buildings; these show the persistence of the collapse along
pre-existing structures and give overall slip rates (1-1.9 cm/year)
similar to the ones calculated for the western portion (1.4-2.3 cm/year).
After the eruption, movement in the western portion decreased significantly,
while parts of the eastern portion continued to creep. The collected
data suggest a model for the spreading of the eastern flank of Etna,
characterized by eruptions along the NE Rift, displacements on a scale
of meters along the western PFS and on a scale of centimeters along
the eastern PFS; the latter then evolves into creeping, while the western
part becomes gradually locked. The new extent of the PFS and its previous
activity indicate that the actively spreading eastern flank continues
below the Ionian Sea floor. Seismic activity during the 2002-2003 deformative
events clustered down at depths 6 km b.s.l., suggesting a deep décollement
for the sliding mass. These data thus suggest a very large gravitational
movement of the eastern flank of the volcano, both on-shore and off-shore.
Keywords:
Mt. Etna; Bocca Nuova; endogenous lava dome; pyroclastic avalanches;
magma ascent
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