Interseismic coupling degree of Serre and Cittanova faults surface in Southern Calabria, (Italy): new constraints from geodetic data observations

Extensional faults in Southern Calabria (Italy) have been widely studied for their capability of generating high magnitude earthquakes (Mw 7-7.2). An example is the historical seismic sequence occurred in 1783, which caused numerous fatalities near the villages located along the longest faults of this region: the Cittanova and the Serre faults. In this work, we estimated the seismic potential of these two faults by a kinematic block modelling approach using GNSS data of both campaign points and permanent stations. Our results indicate that both faults are accommodating the recognized extensional velocity gradient (∼1 mm yr-1) by long-term slip rates (∼2 mm yr-1). To estimate the back slip distribution and the interseismic coupling degree of the Cittanova and Serre faults, we discretized these by a triangular dislocation elements mesh. This approach has allowed us to distinguish the fault areas where elastic seismic rupture is more likely to happen from those affected by aseismic creeping behaviour. The obtained results show that the highest values of coupling are located near the shallow portion of the fault planes and near the southern tip of the Cittanova fault. We therefore estimated a set of possible rupture scenarios finding that the Southern Calabria domain is accumulating an interseismic moment rate at most equal to 2.16 × 1016 Nm yr-1, the equivalent of an earthquake of Mw 4.86 for each year.