Active tectonics of the Adriatic Region

Summary. 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 t o 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 hgh topo-graphic belts that border it on the SW, NW and NE. The relatively rigid behaviour of the Adriatic allows its motion relative t o 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- ; however, these are uncertain by at least a factor of two, and are anyway likely t o be underestimates of the true motion, because of the unknown contribution of aseisniic creep. The Adriatic region resembles, in some ways. other relatively stable conti-nental blocks, such as Central lran 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, bu t is likely t o be located in the Southern Adriatic, near the Strait