Active deformation in Southern Italy, Sicily and southern Sardinia from GPS velocities of the Peri-Tyrrhenian Geodetic Array (PTGA)

Campaign measurement (1995-2000) of Global Positioning System (GPS) site velocities in southern Italy, Central Mediterranean area, document differential displacements within the orogens rimming the Tyrrhenian Sea. Within the Southern Apennines, GPS velocities define two laterally juxtaposed belts of deformation, with transpression in the east and transtension in the west. In the east, ~8 mm/yr convergence between northern Murge-Gargano block and the International GPS System (IGS) site MATE is partitioned across ~east-west striking right-lateral faults, consistent with seismicity and with the offshore geological record. To the south, in northern Calabria, site velocities relative to MATE indicate transpression at ~5 mm/yr, not recorded by seismicity but consistent with the on-land and offshore geological record. In contrast, site velocities along the Tyrrhenian Sea coast to the west diverge from MATE at 2-3.5 mm/yr, and are consistent with the crustal extension documented by seismicity and fault slip studies. The transpressional belt is tracked southward across the Ionian Sea by oblique convergence of central Sicily sites (2-6 mm/yr) relative to the IGS site NOTO in the Hyblean block. North-western Sicily sites display clockwise rotation, a pattern reflected in the geological and paleomagnetic record. Ssignificant horizontal motion accompanies rotation in north-western Sicily and is probably accommodated by west-northwest – east-southeast and northeast-southwest-striking right- and left-oblique faults, respectively, consistent with a regional ~north-northwest – south-southeast trending shortening axis. The ~east-west striking belt of contractional earthquakes observed offshore northern Sicily is consistent with up to ~10 mm/yr geodetic convergence between Sicily and Sardinia. Southern Sardinia sites exhibits differential velocities relative to the IGS site CAGL, suggesting internal deformation which is not recorded by seismicity and might signal incipient fragmentation of the Sardinia margin in response to relative convergence with Sicily.