The impact of structural complexity, fault segmentation, and reactivation on seismotectonics: Constraints from the upper crust of the 2016-2017 Central Italy seismic sequence area

Young and tectonically active chains like the Central Apennines (Italy) are featured by high structural complexity as a result of the overprint of subsequent deformational stages, making interpretation of seismotectonics challenging. The Central Apennines are characterized by the stacking of tectono-sedimentary units organized in thrust sheets. However, extensional tectonics is currently affecting the axial sector of the thrust belt, mostly expressing in extensional earthquakes. Using a large subsurface dataset acquired for hydrocarbon exploration in the region struck by the 2016-2017 Central Italy seismic sequence, we built a comprehensive 3D geological model and compared it with the seismicity. The model primarily shows a series of thrusts developed during the Miocene-Pliocene Apennines orogenesis and inherited normal faults developed during the Mesozoic extensional phase and the Miocene foreland flexural process. These normal faults were segmented and transported within the thrust sheets, and sometimes they still show a clear surface expression. The succession of tectonic stages resulted in a widespread reactivation of inherited structures, sometimes inverting their kinematics with different styles and rates, and disarticulating pre-existing configurations. Such evolution has a strong impact on the seismicity observed in the area, as demonstrated by some examples that show how the seismicity is aligned on segments of inherited faults, both compressional and extensional. Their reactivation can be explained by their favorable orientation within the current extensional stress field. Results feed the debate about the seismogenic potential of faults identified both at depth and surface, which can impact the seismic hazard of the Apennines.

Automated summary

Young and tectonically active chains like the Central Apennines in Italy show high structural complexity due to subsequent deformation stages, with stacking of tectono-sedimentary units organized in thrust sheets and current extensional tectonics affecting the axial sector. A comprehensive 3D geological model built using a large subsurface dataset reveals thrusts developed during the Miocene-Pliocene Apennines orogenesis, inherited normal faults from Mesozoic extensional phase, and Miocene foreland flexural process, impacting seismicity in the area. Reactivation of inherited faults aligned with current extensional stress fields can explain seismicity and debate the seismogenic potential of faults impacting the seismic hazard of the Apennines.