The 2009 LʹAquila earthquake (Italy): Whatʹs next in the region? Hints from stress diffusion analysis and normal fault activity

This work aims at defining the contribution, in terms of earthquake probability assessment, of the integration of Coulomb stress diffusion analysis related to an earthquake with geological studies on fault activities, investigating the case of the April 6, 2009, LʹAquila (central Italy) earthquake (Mw 6.3). The analysis of the Coulomb stress diffusion induced by this earthquake has revealed a stress increase along two poorly-investigated active normal faults in the Apennines: the Subequana fault and the Middle Aterno Valley fault. No strong seismic events have been attributed to these tectonic structures over the past 800–1000 yr, and they have therefore been considered as probable seismic gaps. Geological and paleoseismological investigations have since indicated that these tectonic structures belong to the same 25–30-km-long fault system that ruptured twice during the late Holocene. The last activation occurred between the 4th–1st century B.C. and the past millennium (probably during the 2nd–1st century B.C.), with the penultimate between 6381 ± 30 BP and 3511 ± 37 BP. The data obtained indicate that this fault system might rupture in up to magnitude 6.8 earthquakes and that the 2009 seismic event has brought these tectonic structures about 200 yr closer to failure.