Active crustal extension and strain accumulation from GPS data in the Molise region (central-southern Apennines, Italy)

In this paper, we report new GPS measurements which indicate active NE-SW extension and strain accumulation in the Molise region (Apennines, Italy). The GPS observations were collected during campaigns on benchmarks of the dense IGM95 network (average distance 20 km), spanning a maximum observation interval of 13 years, and have been integrated with measurements from the available permanent GPS sites. Considering the differential motion of the GPS sites, located on the Tyrrhenian and Adriatic coasts, we can evaluate a 4-5 mm/yr extension accommodated across this part of the Apennines. The velocity field exhibits clusters of sites with homogeneous velocity vectors, outlining two main divergence areas, both characterized by the largest velocity gradients: one near Venafro and the other near Isernia where two primary active faults and several historical earthquakes have been documented. These results suggest that an active extension in this part of the Apennines can be currently distributed between the two faults systems associated with the largest earthquakes of this region.