Acocella, Neri and Behncke (2003) Large-scale spreading of the E flank of Mt. Etna (Italy) during the 2002-2003 eruption

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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


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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