Active tectonics of the Adriatic Region

Abstract

Seismicity and fault-plane solutions show that the active deformation in the Adriatic region is very varied. West of Messina, N—S shortening occurs with slip vectors representative of the overall Africa—Eurasia motion. Along the length of peninsular Italy, NE—SW extension on normal faults is the dominant style of deformation, but changes to N—S shortening in N. Italy. Inland central and northern Yugoslavia is deforming on strike-slip and thrust faults, and an intense belt of NE—SW shortening continues south along the coast from central Yugoslavia into Albania. South of Albania the shortening in coastal regions is in a more easterly direction. The most remarkable feature of the region is the low level of seismicity in the Adriatic Sea itself, compared with the intense activity in the high topographic belts that border it on the SW, NW and NE. The relatively rigid behaviour of the Adriatic allows its motion relative to Eurasia to be described by rotation about a pole in N. Italy. Anticlockwise rotation about this pole accounts, in a general way, for the change in style and orientation of the deformation in the circum-Adriatic belts. Historical and recent seismicity account for approximately equal rates of extension in central Italy and shortening in southern Yugoslavia of about 2 mm yr−1; however, these are uncertain by at least a factor of two, and are anyway likely to be underestimates of the true motion, because of the unknown contribution of aseismic creep. The Adriatic region resembles, in some ways, other relatively stable continental blocks, such as Central Iran and the Tarim Basin, that are caught up within the distributed deformation of the Alpine—Himalayan Belt. The Adriatic, however, is bounded on three sides by the relatively stable Eurasia plate. Its boundary with the African plate is short and ill-defined by seismicity, but is likely to be located in the Southern Adriatic, near the Strait of Otranto. The present day seismicity shows that the Adriatic, although once perhaps 'a promontory of Africa', is no longer behaving in this way, and the motions on its boundaries do not directly reflect the Africa—Eurasia convergence.