Constraints On the Seismotectonics of the Central Mediterranean From Very Long Baseline Interferometry

Very Long Baseline Interferometry (VLBI) determined site velocities from seven stations in western Europe reveal a stable continental platform north of the Alps. Deformations between Sweden, Germany and Spain can not exceed 2 mm yr−1. South of the Alps, significant motions are occurring with respect to stable Europe. Two sites east of the Apennine mountains on peninsular Italy have north-east-trending velocities which increase from 2 mm yr−1 in the north at Medicina to 6 mm yr−1 in the south at Matera. In contrast, the VLBI site in the south-eastern corner of Sicily is moving 7 mm yr−1 to the north-north-west. These velocities are largely explained if southern Sicily is attached to a north-westerly moving African Plate and the eastern portion of the Italian peninsula forms part of a hypothesized Adriatic Sea crustal block which is rotating counter-clockwise with respect to Europe about a pole near the Alps. Such an explanation is consistent with the styles of the larger historical earthquakes of the region, which show NE-SW extension across the Apennines, north-south convergence across the Alps, and NE-SW compression in coastal Yugoslavia. the Adria plate model generates 1.5–2.2 × 1018Nm yr−1 of potential earthquake moment along the northern and central Apennines. Historical records suggest that 30–60 per cent of this moment is released seismically. Based on a direct-strain-rate measurement, recurrence intervals for Italian earthquakes south of Medicina are estimated to be 12–46 yr for M6.5+ quakes and 35–143 years for M7.0+ quakes.