High-Resolution Seismic Profiling in the Hanging Wall of the Southern Fault Section Ruptured During the 2016 Mw 6.5 Central Italy Earthquake

The Vettore–Bove normal fault system in central Italy ruptured during the 2016 MW 6.5 Norcia earthquake causing extensive surface faulting. At the Pian Grande di Castelluccio hanging wall basin, along the southern section of the fault ruptured during the MW 6.5 mainshock, we performed a high-resolution seismic reflection/refraction experiment aimed at (a) imaging the shallow pattern of the fault system, and (b) reconstructing the architecture of the continental infill. We collected three profiles for a total length of ∼8 km. We used a reflection processing flow and non-linear refraction tomography to obtain migrated stack sections and P-wave velocity images resolved down to the depth of the pre-Quaternary substratum. The main profile in the northern part of the basin crosses the westernmost splays of the ruptured fault zone striking N150°–170°. Seismic imaging unravels a ∼1 km-wide fault zone comprising three W-throwing splays and subsidiary faults, which affect the continental infill and produce a minimum aggregate Quaternary throw of ∼400 ± 100 m. Recent deformation is localized in this part of the surveyed fault section, attesting active displacement accumulation of the Vettore–Bove fault system. The other profiles in the central-southern part of the basin show additional faults, likely striking N20°–40° and which concurred to generate a ∼500 m-deep depocenter. These faults were mostly active during an early extensional phase; however, one of them likely displaces shallow layers with a throw close to the resolution limit of seismic data (<10 m), suggesting activity in the Late Pleistocene.