Seismic Noise-Based Strategies for Emphasizing Recent Tectonic Activity and Local Site Effects: The Ferrara Arc, Northern Italy, Case Study

During the seismic crisis of May–June 2012, that strongly affected the central sector of the Ferrara Arc, relevant coseismic effects were observed, such as ground deformations and amplification phenomena due to low quality mechanical characteristics of the shallow subsurface (i.e. few hundreds of meters). This portion of the subsurface is not investigated by neither hydrocarbon explorations (too deep) nor geotechnical surveys (too shallow). Furthermore, direct analysis is not cost effective to carry out over such a wide area. To overcome these limitations, we exploited seismic noise-based strategies, which are not invasive and do not require expensive equipment. We carried out several single-station and array measurements (i.e. ESAC, Re-Mi, and HVSR), across some of the major tectonic structures of the eastern Po Plain, belonging to the most advanced buried sector of the Northern Apennines. Such investigations were performed along two profiles, about 27 km-long and oriented SSW–NNE, i.e. almost perpendicular to the regional trend of the Ferrara Arc structures. Our results clearly document lateral shear wave velocity variations and the occurrence of resonance phenomena between 0.52 and 0.85 Hz. Additionally, based on inversion procedures, we were able to infer the depth of the resonant interface(s) and we associated such interface(s) to the major known stratigraphic discontinuities, thus emphasizing the recent tectonic activity of the blind thrusts affecting this sector of the Ferrara Arc.