New geological constraints on the subsurface structure of the 2022 Fano-Pesaro <i>M</i> _w  5.5 earthquake sequence area (Adriatic Sea, Italy) from legacy seismic reflection images and deep well information

Abstract. Studying the subsurface geology in offshore areas is a complex task, as it is impossible or very challenging directly accessing any eventual outcrops at the study site. The integration of key seismic reflection and borehole data is therefore fundamental, even if only available as legacy data on paper hard copy and/or characterized by an apparent low quality. However, such data are often the only ones available, and can still provide a high amount of detailed information for building a reliable geological model to be compared with and discussed about the seismicity distribution in active areas. In this work, legacy seismic reflection profiles calibrated with boreholes are used to propose a new geological model of the frontal part of the Northern Apennines area struck by the 2022 Fano-Pesaro Mw 5.5 earthquake sequence (Adriatic Sea, Italy). The legacy seismic data were digitized and converted to SEG-Y format, and a basic post-stack filtering was applied to enhance data quality. The observed tectonic structures originate from multiple décollements located at different depths and show a strong relationship between the faulting depth and the wavelength of the anticlines. Two structures, namely the Pesaro and the Cornelia anticlines, are interpreted as being related to deep-seated thrusts, showing an en-echelon arrangement and thin-skinned deformation. A smaller wavelength structure, namely the Tamara antiform, is interpreted to be associated with shallow-seated imbricated fore-verging thrusts in the forelimb of the Pesaro anticline. We highlight the importance of constructing a well-constrained geological model by integrating legacy geological and geophysical data, aimed at studying offshore seismotectonic settings.