Present-day tectonics in and around the Adria plate inferred from GPS measurements

Movement of the Adria microplate is one of the main elements for understanding crustal deformations in the central Mediterranean and central Europe. To study present-day tectonics in Adria and the nature of its boundary relative to those of the Africa and Eurasia plates, three GPS (Global Positioning System) campaigns involving 41 stations were carried out within CRODYN (the Croatian and Slovene Geodynamic Network). Movement of stations derived in the International Terrestrial Reference Frame 1996 (ITRF96) with respect to the permanent ITRF/IGS (International GPS Service) station GRAZ in Austria, located north of the network, and values of the principal strain rates determined on the basis of analytical surface deformation theory suggest that Adria is divided into three different deformation zones (northern, central, and southern). The domain of northeastern Italy moves 5 mm/yr in an east-northeast direction. The stations in southwestern Slovenia move 3-7 mm/yr in a north-northwest direction, whereas those in southern and northeastern Istria move 4-5 mm/yr in a more easterly direction. The greatest movement (8-10 mm/yr) occurs in central Adria between the Gargano zone and the central Dinarides ; there, the movement is northeastoriented. A fragmentation of Adria into subblocks linking the Gragano zone to the central Dinarides cannot be clearly demonstrated. The southeastern part of Adria, along the coastline of Albania, moves 5-7 mm/yr in an almost east-west direction, and eastern Albania moves 6 mm/yr in an east-southeast direction. The permanent ITRF/IGS stations POTS and WTZR in Germany, BOR1 in Poland, and PENC in Hungary demonstrate no significant movement. The movement of the stations discussed here differs very clearly from the known north-west motion of the Africa plate and suggests that Adria is an independent microplate.