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[1] Broad geological and geophysical documentation is available on regional extensional systems driven by low-angle normal faults. However, little information exists about the three-dimensional geometry and the offset distribution of such extensional structures. We present a new set of balanced geological sections across the extensional fault system driven by the Altotiberina low-angle normal fault in the Northern Apennines of Italy. We document this extensional system throughout a large set of surface (field surveys and geological maps) and subsurface data (seismic reflection profiles and boreholes). The subsurface data allowed us to define the fault deep geometry and to obtain its structural contours. The fault geometry is characterized by both along-dip and along-strike irregularities. In cross-section, the fault displays a staircase trajectory with the shallowest part being dome-shaped and flattened to horizontal. This bending could be due to the footwall uplift triggered by a footwall uploading greater than about 115 MPa. The sequential restoration of five geological cross-sections yields a maximum extension of about 10 km accumulated over approximately 3 Ma. The resulting long-term slip-rate is about 3 mm/yr, which is of the same order as the present-day extensional rate measured by GPS (2.5-3.0 mm/yr), suggesting an almost steady state extension over the last 3 Ma. The distribution of the extension values along the fault strike is bell-shaped, as expected for a continuous surface.

Starting from 24 August 2016, a long seismic sequence, including nine Mw > 5.0 earthquakes, struck a wide area of the Central Italy. A large amount of geological, geodetic, and seismological data envisages a complex system of NNW‐SSE trending, seismogenic normal faults. These active tectonic structures are well known at the surface and consistent with previous seismotectonic studies. In order to improve the comprehension of the seismotectonic framework of this seismic sequence, we provide a novel reconstruction of the subsurface geology of the area close to the Norcia Mw 6.5 mainshock (30 October 2016), based on previously unpublished seismic reflection profiles and available geological data. All the data have been synthesized along a 47 km long, WSW‐ENE trending geological cross section, interpreted down to a depth of 12 km. Comparing the subsurface geological model with the available seismological data, we find that the majority of seismicity is confined within the sedimentary sequence and does not penetrate the underlying basement. The basement has been constrained at depths of 8 to 11 km and coincides with the cutoff of the seismicity. We have also traced the trajectories of the seismogenic normal faults activated during this seismic sequence, reconciling the high‐angle (dip>65°) normal faults exposed at the surface, with their angle (dip < 50°) at hypocentral depths. The results of this study may be useful for better understanding the rheological properties of the seismogenic rock volume, as well as the coseismic deformations of the topographic surface observed by geodetic techniques and field mapping.

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