The Palermo (Sicily) seismic cluster of September 2002, in the seismotectonic framework of the Tyrrhenian Sea-Sicily border area

G. Giunta, D. Luzio, E. Tondi, L. De Luca, A. Giorgianni, G. D'Anna, P. Renda, G. Cello, F. Nigro, M. Vitale

Abstract


The northern coast of Sicily and its offshore area represent a hinge zone between a sector of the Tyrrhenian
Basin, characterized by the strongest crustal thinning, and the sector of the Sicilian belt which has emerged. This
hinge zone is part of a wider W-E trending right-lateral shear zone, which has been affecting the Maghrebian
Chain units since the Pliocene. Seismological and structural data have been used to evaluate the seismotectonic
behavior of the area investigated here. Seismological analysis was performed on a data set of about 2100 seismic
events which occurred between January 1988 and October 2002 in the Southern Tyrrhenian Sea. This paper
focuses in particular on a set of data relating to the period from 6th September 2002, including both the main
shock and about 540 aftershocks of the Palermo seismic sequence. The distribution of the hypocenters revealed
the presence of two main seismogenic zones. The events of the easternmost zone may be related to the Ionian
lithospheric slab diving beneath the Calabrian Arc. The seismicity associated with the westernmost zone is closely
clustered around a sub-horizontal regression plane contained within the thinned Southern Tyrrhenian crust,
hence suggesting that this seismogenic zone is strictly connected to the deformation field active within the hinge
zone. On the basis of both structural and seismological data, the brittle deformation pattern is characterized by
high-angle faults, mainly represented by transcurrent synthetic right-lateral and antithetic left-lateral systems,
producing both restraining/uplifting and releasing/subsiding zones which accommodate strains developing in response
to the current stress field (characterized by a maximum axis trending NW-SE) which has been active in
the area since the Pliocene. The cluster of the seismic sequence which started with the 6th September 2002's
main shock is located within the hinge zone. The distribution of the hypocenters relative to this sequence emphasizes
the presence of a high-angle NE-SW-oriented deformation belt within which several shear surfaces are
considered to be found sub-parallel to that established for the main shock. The kinematics of all these structures
is consistent with a compressive right-lateral focal mechanism.

Keywords


seismotectonics;Southern Tyrrhenian Sea;Northwestern Sicily

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References


DOI: https://doi.org/10.4401/ag-3373
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X