Detailed image of crustal structure in the southern Apennines-Calabrian Arc border region from local earthquake tomography

We present a new seismic velocity model for the southern Apennines - Calabrian Arc border region aiming to better define the crustal structures at the northern edge of the Ionian subduction zone. This sector also includes the Pollino Mts area, where a seismic sequence of thousands of small to moderate earthquakes has been occurring since spring 2010 (Presti & al., 2013; Totaro & al., 2013). To perform the tomographic inversion, we selected ca. 3500 earthquakes occurred in the last thirty years and recorded by permanent and temporary networks managed by INGV and Calabria University. Using the LOTOS code for passive tomography inversion (Koulakov, 2009), we have computed the distribution of Vp, Vs, and the Vp/Vs ratio. The obtained velocity models, jointly evaluated with results of synthetic modeling, as well as with the hypocenter distribution and geological information, give us new constraints to geodynamical and structural knowledge of the study area. In particular, in the upper crust a low-velocity anomaly of P- and S-waves is detectable beneath the Pollino Mts area and seems to separate the two domains of Calabrian Arc and southern Apennines, characterized by higher velocity values. The distributions of high Vp/Vs ratio in the upper crust clearly correlate with areas of huge seismicity, corresponding to strongly fractured rocks with high fluid content. In the lower crust we detect a clear transition from high to low seismic velocities in correspondence of the Tyrrhenian coast of the study area which may represent the transition from oceanic to continental crust.