Abstract

Global Positioning System (GPS) velocities indicate that Adria no longer behaves as a rigid tectonic indenter into southern Europe and is divided into northwestern and southeastern velocity domains. Differential motions are recognized in a velocity field determined from the Peri-Tyrrhenian Geodetic Array (PTGA) and International GPS Service (IGS) sites in the circum-Tyrrhenian region of the central Mediterranean and published GPS velocities from the eastern Adriatic coast. In a fixed Eurasian reference frame, PTGA and IGS site velocities in Sicily and southern Italy are as much as 10 mm/yr in a northward direction, similar to GPS velocities along the eastern coast of the Adriatic Sea. In contrast, velocities in northern Italy are small or statistically insignificant and similar to velocities in Sardinia and Corsica outboard of western Adria. The tectonic boundary dividing Adria is seismically active and passes around the southern and eastern margins of the Tyrrhenian Basin, crosses central Italy, extends into the Adriatic Sea, and follows the western margin of the Dinaride tectonic belt north to the Gulf of Venice. The eastern margin of Adria is approximately located and follows the axis of the central Dinaric Alps southeast to the Hellenic arc. Southeastern Adria has a velocity related to northward motion of Africa, whereas northwestern Adria has negligible differential motion in the Eurasian frame and now is part of the Alpine collage of southern Europe.

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