Fossil landscapes and youthful seismogenic sources in the central Apennines: Excerpts from the 24 August 2016, Amatrice earthquake and seismic hazard implications

We show and discuss the similarities among the 2016 Amatrice (Mw 6.0), 1997 Colfiorito-Sellano (Mw 6.0-5.6) and 2009 L’Aquila (Mw 6.3) earthquakes. They all occurred along the crest of the central Apennines and were caused by shallow dipping faults between 3 and 10 km depth, as shown by their characteristic InSAR signature. We contend that these earthquakes delineate a seismogenic style that is characteristic of this portion of the central Apennines, where the upward propagation of seismogenic faults is hindered by the presence of preexisting regional thrusts. This leads to an effective decoupling between the deeper seismogenic portion of the upper crust and its uppermost 3 km. The decoupling implies that active faults mapped at the surface do not connect with the seismogenic sources, and that their evolution may be controlled by passive readjustments to coseismic strains or even by purely gravitational motions. Seismic hazard analyses and estimates based on such faults should hence be considered with great caution as they may be all but representative of the true seismogenic potential.