New insights on 3D crustal structure in southeastern Sicily (Italy) and tectonic implications from an adaptive mesh seismic tomography

The adaptive mesh double-difference tomography algorithm (tomoADD) was applied to absolute and differential P, S and S–P data to determine three dimensional VP, VS and VP/VS variations and event locations in southeastern Sicily (Italy).The obtained velocity images highlight vertical and lateral heterogeneities that can be associated with different geological units and main tectonic features. In particular, the sharp velocity contrasts are consistent with previously recognized active faults, allowing us to better determine their shapes and geometries at depth.Moreover, a striking correspondence between areas ruptured by earthquakes and velocity anomalies is observed. In fact, seismicity is mostly confined in the high velocity volumes and/or along the high–low velocity boundaries at mid-crustal depths, whereas it tends to avoid regions with lower than average VP and VS values and higher VP/VS ratios.