Fault Interaction During Large Earthquakes as Revealed by the L’Aquila 2009 Sequence

The geological and structural heterogeneity of the crust exerts a primary control on the development of large earthquakes and seismic sequences. The Central Apennines is a clear example of how earthquake occurrence is entangled with the complexity of the upper crustal structure. In this study, we make new inferences on this interaction for the 2009 L’Aquila seismic sequence, combining geological and structural data with 3D high-resolution V_p and V_p/V_s velocity models. The pervasive segmentation of normal faults inherited from the Pliocene compression is a primary factor that controls the evolution of large ruptures. We propose that geometrical heterogeneity and misorientation of fault segments pervading thrust sheets conditioned the dynamic interaction during the rupture evolution. Our results emphasize how the structural legacy of previous tectonics influences fault activation. Pre-existing heterogeneous structures compartmentalize fluid-filled volumes, which control the development of coseismic ruptures and the spreading of aftershocks. These findings raise questions about the challenges of directly correlating surface observations and aftershock data with fault length and call for a reassessment of the seismic hazard of the Central Apennines.