The influence of subsurface geology on the distribution of earthquakes during the 2016-–2017 Central Italy seismic sequence

In 2016–2017, a destructive sequence of earthquakes affected a wide portion of Central Italy, activating a complex, 80-km long system of SW-dipping normal faults and causing impressive surface faulting and widespread damage. Former studies providing reconstructions of the fault systems activated during this sequence, are mostly based on high-resolution seismological and geodetic data. In this paper, we integrate surface and subsurface geological data with the ones obtained by an irregular network of seismic reflection profiles, aimed at providing a comprehensive reconstruction of the subsurface lithologies and structures in this area. We have constructed a set of five geological cross-sections, passing through the mainshock epicentral areas (Mw > 5.5) of the seismic sequence. The cross-sections are extrapolated down to a depth of ca. 12 km, along which we have plotted relocated seismicity. Combined geological and seismological data support a new 3D seismotectonic model, illustrating the propagation through time and space of the seismic ruptures during the sequence. Our results show that the litho-mechanical stratigraphy exerted a primary control on the distribution of seismicity, as it is mostly hosted in the more competent lithologies (i.e. the Late Triassic-Paleogene succession, consisting of carbonates and evaporites). In addition, we illustrate the crucial role played by the inherited compressional structures in determining the lateral and vertical variations of the rheological properties of the upper crust and, eventually, the overall geometry and segmentation of the seismogenic extensional system. The workflow proposed here can be applied to other seismogenic zones throughout the world, since reliable seismotectonic models require an accurate reconstruction of the subsurface geological setting, based on a close integration of geological, geophysical and seismological data.