High-Resolution Densely Spaced Wide-Aperture Seismic Profiling as a Tool to Aid Seismic Hazard Assessment of Fault-Bounded Intramontane Basins: Application to Vallo di Diano, Southern Italy

Seismic hazards in extensional regions are mostly posed by high-angle
normal faults and deep hanging-wall basins that can promote significant groundmotion
amplifications. Characterized by strong lateral velocity variations, these structures
represent challenging targets for seismic exploration. In this paper, we show that
prestack depth migration of high-resolution seismic-reflection data, collected with
nonconventional dense wide-aperture arrays, can effectively assist deterministic
seismic-hazard assessment of fault-bounded basins. Our high-resolution 3.2 km long
seismic profile was acquired along Vallo di Diano, the largest fault-bounded intramontane
basin in the southern Apennines seismic belt (Italy). The imaging strategy combines
prestack depth migration with an iterative velocity-building technique that
utilizes results of multiscale refraction tomography. In particular, migration of steeply
dipping reflections is essential in imaging the complex morphology of the basement
rocks beneath the basin. By combining seismic-reflection and VP tomography results
we were able to evaluate (1) the structure of the Vallo di Diano basin along a representative
transect from near-surface to basement depths; (2) the shallow-depth geometry
of the Vallo di Diano fault system, which bounds the basin to the east; (3) the
structure of the sediment–basement interface; and (4) the velocity structure of basement
and sediments within the basin. These findings are valuable both for understanding
the tectonic evolution of the Vallo di Diano and for developing earthquake-shaking
scenario studies.