Rates of active compressional deformation in central Italy and Sicily: evaluation of the seismic budget

Historical and recent seismicity records and available source mechanisms in eastern-central Italy (Marche-Adriatic region), in mainland-southern Sicily and in the Tyrrhenian offshore of northern Sicily show comparable deformation patterns. Seismotectonic considerations indicate that each of the three areas represents a broad seismogenic province of relatively homogeneous deformation. On the basis of the historical earthquake catalogue, the parameters of the Gutenberg-Richter distribution have been calculated by means of a Monte Carlo simulation method. The average moment tensors have been computed from focal mechanism data and the strain rate and velocity tensors evaluated by means of Kostrov's (in Izv Acad Sci USSR Phys Solid Earth 1:23-44, 1974) relation, which also considers the shape and size of the seismogenic volume. The uncertainties have been systematically incorporated. The results show that the three seismotectonic provinces are all undergoing shortening at seismic rates (similar to 0.3 mm/year in the WSW-ENE direction in the eastern Marche-Adriatic region, similar to 0.1 mm/year in the N-S direction in mainland-southern Sicily and similar to 0.2 mm/year in the NW-SE direction in the Southern Tyrrhenian zone). The motion pattern in the Marche-Adriatic and in the Sicilian provinces suggests that these areas undergo active crust-scale deformation along reverse shear zones, in agreement with recent horizontal GPS motion model and other independent evidence.