Active Extension and Contraction in the Southern Apennines Orogenic Belt, Italy Derived from GPS Velocities of the Peri-Tyrrhenian Geodetic Array

A velocity field determined for 13 GPS sites of the Peri-Tyrrhenian Geodetic Array located in the Southern Apennines, the Apulian foreland, and the Calabrian arc of southern Italy is consistent with simultaneous extension and contraction within the orogen. GPS sites located in bedrock were occupied in 1995, 1997, and 2000 for 18 to 24 hours during each campaign. The GPS data were processed using BERNESE (4.2) in the IRTF97 realization using continuous GPS sites at Matera in southern Italy, Noto in southern Sicily, and Cagliari in Sardinia for reference. In a reference frame fixed on Matera in the southern Apulian foreland, sites along the Tyrrhenian coast are consistent with active seismicity and reflect crustal extension. The sites along the Tyrrhenian-margin are moving SW at 2-6 mm/yr, with the highest rates along the coast and decreasing easterly in the Apenninic highlands. Within the medial zone of the Apennines, located along the physiographic interface between the carbonate highlands of the Apennines and the subdued topography of the deformed synorogenic rocks of the foreland, localized convergence (6 mm/yr) and divergence (8-9 mm/yr) occur along a NNW-SSE axis. In the south, two sites move NNE at 3-4 mm/yr and converge on a site farther north moving SSE at 3 mm/yr. The northern-most site lies north of a NE trending fault system and diverges from the central medial zone with a NNW velocity of 6 mm/yr. GPS sites in the Apulian foreland northeast of Matera are moving west. Velocities decrease from south to north from 7 to 4 to ~1 mm/yr from the Murge platform to Gargano. GPS velocities and seismicity indicate that the Apulian foreland is decoupled from the basement and actively deforming as part of a system of structures underlying the Adriatic Sea. Differential motion between the Apulian foreland and the medial zone is consistent with right-transpression. Simultaneous shortening and extension within the medial zone may be associated with arcuation of the frontal thrust belt. Orogen normal extension along the Tyrrhenian margin is probably related to crustal delamination and formation of seafloor in the Tyrrhenian Sea.