Insights on the seismotectonic of Calabria-Lucania border region (Southern Italy): different tectonic styles at different depths

The Calabria-Lucania border region represents the transitional area between the Southern Apennines and the Northern sector of the Calabrian arc. Roughly the whole Apennine chain is struck by more or less intense earthquakes. While the northern and central parts of the chain are characterized by foreland contraction and hinterland extension, the Southern Apennine is characterized by a strike-slip kinematics in the eastern sector and by an extensional regime in the western sector. Strike-slip earthquakes have been observed also in the axial part of the Campania-Molise Apennines, rightly beneath the active extensional sector.

The Calabria-Lucania border region is considered a seismic gap in the Apennine chain; few paleo-earthquakes, with magnitude ranging from 5 to 7, have been recorded in the area. During 2010-2014 the region was affected by a low-moderate instrumental seismicity (known as Pollino seismic sequence): thousands of earthquakes occurred. Analysis of that seismicity revealed a shallow hypocentral distribution located into the first few km below the surface, and focal mechanisms of the strongest events of the sequence are consistent with upper crustal extensional deformation. While the shallow seismicity of Calabria-Lucania border region has been deeply studied after the 2010-2013 sequence, the sporadic deep seismicity needs a more detailed analysis.

As highlighted by previous studies, instrumental seismicity recorded from 2013 to 2015 reveals the presence of a sporadic deep (from 9 to more than 20 km) seismicity. The events located between 9 and 17 km deep have transcurrent to transpressional kinematics with NE-SW trending P axes; while deeper events show a strike-slip kinematics with NW-SE trending P axes.

We analyzed deep (> 10 km) seismicity recorded in the area from 2013 to nowadays. Starting from the picking of seismograms of more than 40 events (with M between 2.4 and 3.8), we analyzed the focal mechanisms of events computed using at least six good first motion observations. According to Ferranti et al., 2017, our results highlight the presence of a strike-slip/oblique kinematics at depths of more than 20 km. Between 10 and 20 km depth both dip-slip and strike-slip kinematics are present, with a predominance of the last ones, confirming the presence of a transition zone.  

Finally, we inverted the focal mechanisms dataset to infer about the stress field active in the region.