Etna flank dynamics: A sensitivity analysis by numerical modelling - Volcanic Rock Mechanics - page 140

etna flank dynamics: a sensitivity analysis by numerical
modelling

T. apuani
Dipartimento di Scienze della Terra “A. Desio”, Università degli Studi di Milano, Milan, Italy

c. corazzato
Dipartimento di Scienze Geologiche e Geotecnologie, Università degli Studi di Milano-Bicocca, Milan, Italy

aBsTRacT: The present work investigates the flank deep instability dynamics of Mount etna volcano
by means of bi-dimensional numerical modelling, comparing finite element and finite difference methods,
and by limit equilibrium analysis. The complicated conceptual model was first simplified and progres-
sively implemented with a sensitivity analysis to evaluate the effect of topography, geometry and rheologi-
cal behaviour of the structural units. The model is then implemented considering the presence of magma
pressure along the feeding system. The results are expressed in terms of stress-strain field, displacement
pattern, plasticity states and shear strain increments, or factor of safety.

1 inTRoDUcTion the eastern and south-eastern flank (Borgia et al. ,

1992; Tibaldi & Groppelli, 2002; corazzato &
Tibaldi, 2006). To the north, the boundary of such
unstable sector is represented by the e-W trend-
ing Pernicana Fault system (azzaro et al. , 1998;
acocella & neri, 2005; neri & al., 2003; and refer-
ences therein) extending from the ne Rift to the
coastline, with a predominant left-lateral motion.
here the flank shows a predominant ese slip. To
the south, the slip of the flank appears less consist-
ent, being directed towards se and s, and control-
led by several structures, with different geometry
and kinematics (Rasà et al. , 1982; Groppelli &
Tibaldi, 1996, 1999; Monaco et al ., 1997; azzaro
et al. , 1998).
The instability is long-duration and apparently
steady-state, although with documented accelera-
tions related to magma pressure and with differen-
tial movements within the unstable mass (Rust &
neri 1996; acocella et al. , 2003; acocella & neri,
2005; Bonforte & Puglisi, 2006).

Most active volcanoes show clear evidence of flank
instability resulting from several interacting causes
including gravity force, magma ascent along the feed-
ing system, and local and/or regional tectonic activ-
ity (Voight et al. , 1981, 1983; elsworth & Voight,
1995; iverson, 1995; McGuire, 1996; Voight &
elsworth, 1997; elsworth & Day, 1999; Voight,
2000). The complexity of such dynamics is still an
open subject of research.

1.1 Geological-structural setting
The present work focuses on the dynamics of Mount
etna, the largest active european stratovolcano,
located on the eastern coast of sicily (southern italy,
Fig. 1 ) . it rises above a complex regional tectonic
framework, dominated by a n-s trending direction
of maximum compression, due to the eurasia-africa
plates collision, where the hyblean plateau is sub-
ducted beneath the apennine-Maghrebian thrust
chain, and a related e-W trending direction of maxi-
mum extension, associated with the development of
the Malta escarpment, the possible surface expres-
sion of a tear in the subducting ionian slab (lentini
et al. , 1996). on the eastern flank of etna, the Pleis-
tocene subetnean clay unit is interposed between the
apennine-Maghrebian flysh units and the volcanic
edifice products (Di stefano & Branca, 2002).
several volcanotectonic elements, represented
by both rift zones and faults, influence the volcano
dynamics ( Fig. 1 ) . a deep-seated instability affects

1.2 The approach
as a contribute to understand the etna eastern
flank dynamics, a stability analysis was performed,
aimed first at evaluating the role of basement
geometry and rheological characters, in terms of
constitutive law and the associated strength and
deformability properties, and then at exploring the
effect of magma pressure.
The problem was first approached by limit equi-
librium analyses (leM), and then by numerical