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Dario Albarello, Enzo Mantovani and Marcello Viti
above phenomenon is connected with an active can be used to simulate the mechanical be-
1ifting process. Other authors (Channell and haviour of shallow crustal bodies. In the area
Mareshal, 1988; Argnani, 1993) hypothesized here considered, the reliability of this approxi-
that the troughs in the Sicily Channel opened mation is supported by the interpretation of
up in response to a NEward drifting of Sicily, gravimetrie and structural data, which indicates
driven by «slab pull» mechanisms. Mantovani the significant role played by the elastic flexu-
et al. (1996, 1997) argued that the above two ral behaviour of the upper crust in the recent
hypotheses can hardly account for the time structural evolution at the scale length of tens
space distribution of compressional and exten- of kilometres (Royden and Karner, 1984;
sional deformation events in the Centrai Moretti and Royden, 1988; Cogan et al., 1989;
Mediterranean zone, with particular regard to Albarello et al., 1990; Barrier, 1992) compara-
the Tyrrhenian-Maghrebian system, the Cal- ble with lithospheric mechanic thicknesses de-
abrian are and the Northern African margin, duced for the Mediterranean area by rheologi-
and for the kinematics of the confining major cal models (Viti et al., 1997).
blocks, i.e., Africa, Adriatic and Eurasia.
The above authors suggested instead that the Further simplifications can be introduced in
deformation pattern in Sicily and surrounding the model if one assumes that tectonic pro-
zones is mainly related to the convergence be- cesses are mostly related to horizontal tectonic
tween Africa and Adriatic forelands which forces, induced by the relative motions of ma-
is assumed to occur along a SSW-NNE direc- jor plates. The evidence and arguments which
tion (Albarello et al., 1993, 1995). The short- can support this hypothesis are reported by
ening required by this plate convergence is ac- Mantovani et al. (1996, 1997). This assump-
commodated by lateral escapes of crustal tion implies that a 2D piane stress approxima-
wedges, whose relative motions with respect to tion should not involve important deviations
the surrounding zones cause the observed pat- from reality in modelling the displacement and
tern of compressional, tensional and transcur- strain fields in the study area. A quite similar
rent features. This work describes an attempt to approach has been adopted by other authors
quantify, by finite element calculations, the (Kasapoglu and Toksoz, 1983; Shachinger,
major consequences, in terms of strain and dis- 1992; Grunthal and Stromeyer, 1992) to simu-
placement fields, of the above geodynamic hy- late the tectonic stress field in Centrai Europe
pothesis. The results obtained by numerica! ex- and the Eastern Mediterranean.
periments are then compared with observed
features. Geologica! and geophysical evidence in the
considered area suggests that an important role
2. Modelling approach in the recent evolution has been played by ma-
jor active margins and transform faults in ac-
A realistic modelling of tectonic processes commodating the relative motions between rel-
in continental collision zones is a very difficult atively undeformed blocks (Finetti and Del
task, given the high complexity of crustal de- Ben, 1986; Reuther et al., 1993; Ben Avraham
formation processes which affect continental and Grasso, 1990). This hypothesis is also sup-
lithospheric structures characterized by rheo- ported by some recent experimental results
logical stratification and strong lateral het- (Ratschbacher, 1991; Sornette et al., 1993) and
erogeneities (Meissner, 1986; Ranalli, 1987). theoretical considerations which have stressed
However, some simplifications can be adopted the importance of large faults in controll-
if the analysis is limited to the study of short ing tectonic processes (Thatcher, 1995; Twiss
time intervals (hundreds of years), i.e., those et al., 1993).
involved by seismogenic processes. In this
case, deformations can be considered small On the basis of the above evidence and ar-
everywhere, and thus the elastic approximation guments, we approached the modelling by as-
suming that the system is constituted by poorly
deformable blocks separated by major tectonic
belts, where most deformation is accommo-
dated. Poorly deformable blocks are simulated
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