Subsurface imaging in urban environments: Insights from multi-method geophysical surveys in the historical center of Messina (southern Italy)

The city of Messina, southern Italy, is characterized by high seismic hazard and complex near-surface conditions. Messina has been repeatedly struck by destructive earthquakes over the last centuries, most notably the M7.1 event of 1908, which caused near-total destruction. Reconstructions following these earthquakes generated thick and laterally non-uniform anthropogenic deposits (rubble and debris) that, combined with vertically heterogeneous stratigraphy, might pose significant challenges for accurate subsurface characterization and site response analysis. In this study, we performed integrated geophysical surveys in the historical center of Messina, focusing on the area surrounding the Cathedral, where urban stratigraphy is strongly influenced by both natural and anthropogenic processes. Ambient noise data were analyzed using the Horizontal-to-Vertical Spectral Ratio technique to estimate fundamental resonance frequencies and delineate major impedance contrasts. Active and passive surface-wave methods, including Multichannel Analysis of Surface Waves and array-based approaches, were employed to retrieve shear-wave velocity profiles at different depths. The combined results allowed the identification of key stratigraphic interfaces, the recognition of laterally variable anthropogenic fills and deposits, and the estimation of the main discontinuities within the uppermost layers. These findings demonstrate the effectiveness of a multi-method approach in resolving shallow subsurface complexity in highly urbanized areas. The outcomes provide essential input for seismic microzonation, site response modeling, and hazard mitigation strategies in one of the most seismically vulnerable urban environments of the central Mediterranean.