Response of ancient inherited structures to new seismic sequence: insides the central Apennines.

The central Apennines present complex fault structures resulting from the superposition of different tectonic phases. During the Lower Mesozoic the area was part of the passive margin of the Tethys; from the Miocene the area underwent a change of deformation regime associated with the collision between Africa and Europe. This phase went on until the middle Pleistocene building a thrust belt and related foreland basin. Since the late Pleistocene the axial zone of the thrust belt is undergoing extensional tectonics as demonstrated by the recent most earthquakes in the area (L’Aquila 2009, Central Italy, 2016). Given the complex structure of the Apennines, interactions between different fault systems cannot be excluded. For this reason, we modeled alternative fault geometries in order to determine which may be the most consistent with the measured ground deformation associated with the L’Aquila earthquake. Merging literature data, more than 50.000 relocated events (INGV courtesy) and the main focal mechanisms, we built a 3D geological model of the main fault responsible for the L'Aquila 2009 earthquake. Taking advantage of numerical models, we tested different plausible fault configurations comparing the surface deformation obtained from the numerical models with InSAR data. The model with active fault that daylights produces surface deformation that greatly exceeds that observed from geodesy; results of other models are consistent with the presence of blind faults (upper tip ~ 2 km depth). A set of alternative fault geometries that include different degrees of reactivation of secondary faults have been and will be modeled. The results of these models represent a wide range of cases that can help us to better understand how buried faults can affect surface deformation and how they can interact with pre-existing discontinuities.