Seismic hazards in extensional regions are mostly posed by high‐angle normal faults and deep hanging‐wall basins that can promote significant ground‐motion 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.