Building up a subsurface geological model in active offshore areas: constraints from legacy seismic reflection profiles and deep wells in the 2022 Fano-Pesaro Mw 5.5 earthquake sequence area (Adriatic Sea, Italy)

Abstract. Building a geological model in offshore areas is a complex task, due to the obvious absence of outcrops and thus the inaccessibility to 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 compare and discuss with 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 observed tectonic structures are originated by multiple décollements located at different depths and show a strong relationship between the faulting depth and the anticlines wavelength. Two structures, namely Pesaro and Cornelia anticlines, are interpreted as related to deep-seated thrusts, showing an en-echelon arrangement and thin-skinned deformation. A smaller wavelength structure, namely Tamara antiform, is interpreted to be related to 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 offshore seismotectonic studies as well as at industrial applications, particularly in the context of energy transition.