The seismotectonic role of transversal structures in the Plio-Quaternary evolution of the External Marche Apennines (Italy)

The seismotectonic setting of external Marche Apennines (Central Italy) was defined integrating geomorphological, structural, and seismological data. Strong historical earthquakes characterized the area, but geometries and kinematics of the seismogenic sources are not well defined. Plio-Quaternary Apennine compressional NW-SE structures are segmented by NE-SW oriented transversal faults, whose origin and role are still debated. We characterize the geometry, kinematics, and activity of four main transversal faults to better define their seismogenic potential. These high-angle and deeply rooted transversal fault systems have been mapped; they separate the external Apennine sector into blocks and sub-blocks with different structural and evolutionary features. The integrated dataset revealed that some inherited fault segments have recently been reactivated displacing Quaternary deposits. Spatial distribution of seismicity indicates that some clusters of hypocentres are located within the basement. Stress field analysis using available focal mechanism solutions confirms the prevalence of left-lateral kinematics on roughly SW–NE oriented structures. The transversal structures thus contribute to the longitudinal segmentation of the Apennine structures and, more in general, they are involved in the northern part of Adria plate kinematics toward N and NNW. Assessing seismic hazard and planning to mitigate risk in populated areas close to the Adriatic coast should consider these potentially active faults evidenced by the instrumental seismicity and important historical earthquakes.