Ambient vibration analysis contribution to the subsurface geological model definition for the Sulmona intermontane basin: (Central Italy)

Defining the deep geometry of sedimentary basins characterized by strong lateral heterogeneity and limited subsurface constraints remains a key challenge in engineering geology and seismic microzonation. This study presents an integrated methodological framework based on ambient vibration techniques to constrain the subsurface geological model of the Sulmona intermontane basin (Central Italy). The study area is a tectonically active half-graben filled with thick Quaternary continental deposits, bounded by the high-hazard Mt. Morrone fault system. Our approach combines extensive single-station Horizontal-to-Vertical Spectral Ratio (HVSR) measurements, passive seismic array investigations, borehole stratigraphic data, and detailed geological mapping. The joint interpretation of these datasets allows the construction of laterally constrained geological cross-sections and an interpolated basin-scale representation of the bedrock interface. A simplified 1D resonance model has been preliminary adopted to relate fundamental frequency, average shear-wave velocity Vs, and sediment thickness, then acknowledging its limitations in complex tectonic settings affected by faulting, velocity inversions, and facies transitions where complex 2D basin effects take place. The results reveal a complex bedrock morphology with sediment thicknesses reaching up to 800–900 m in the southern depocenter. The proposed methodology demonstrates how ambient vibration data, when calibrated with independent geological and geotechnical information, effectively supports the reconstruction of large-scale basin models. The workflow is particularly suited for preliminary seismic hazard assessment and engineering applications, providing a robust basis for targeted geognostic investigations and advanced numerical seismic-response modeling in urban areas under high seismic risk.