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 Mediterraneanarea, document differential displacements within the orogens rimmingthe Tyrrhenian Sea. Within the Southern Apennines, GPSvelocities define two laterally juxtaposed belts of deformation, withtranspression in the east and transtension in the west. In the east,~8 mm/yr convergence between northern Murge-Gargano block andthe International GPS System (IGS) site MATE is partitioned across~east-west striking right-lateral faults, consistent with seismicityand with the offshore geological record. To the south, in northernCalabria, site velocities relative to MATE indicate transpression at~5 mm/yr, not recorded by seismicity but consistent with the on-landand offshore geological record. In contrast, site velocities along theTyrrhenian Sea coast to the west diverge from MATE at 2-3.5 mm/yr,and are consistent with the crustal extension documented by seismicityand fault slip studies. The transpressional belt is tracked southwardacross the Ionian Sea by oblique convergence of central Sicilysites (2-6 mm/yr) relative to the IGS site NOTO in the Hyblean block.North-western Sicily sites display clockwise rotation, a patternreflected in the geological and paleomagnetic record. Ssignificanthorizontal motion accompanies rotation in north-western Sicily andis probably accommodated by west-northwest – east-southeast andnortheast-southwest-striking right- and left-oblique faults, respectively,consistent with a regional ~north-northwest – south-southeasttrending shortening axis. The ~east-west striking belt of contractionalearthquakes observed offshore northern Sicily is consistent with upto ~10 mm/yr geodetic convergence between Sicily and Sardinia.Southern Sardinia sites exhibits differential velocities relative to theIGS site CAGL, suggesting internal deformation which is notrecorded by seismicity and might signal incipient fragmentation ofthe Sardinia margin in response to relative convergence with Sicily.