Geometry and evolution of the Middle Aterno Quaternary basin and relationship with the 2009 L'Aquila earthquake causative fault system (Abruzzi Apennines, Italy)

An Mw 6.1, devastating earthquake, on April 6, 2009, struck the Middle Aterno Valley (MAV) (Abruzzi Apennines, Italy) due to the activation of a poorly known normal fault system.

We combined different geophysical investigations methods (i.e. deep ERT profiles, time domain electromagnetic soundings and single-station ambient vibration surveys) to image the subsurface 3-D geometry of the Quaternary continental infill of the MAV. We integrated this dataset with the structural analysis of the outcropping fault population and with the absolute dating and description of the stratigraphic relationships of the Quaternary continental deposits to reconstruct the long-term, tectono-sedimentary evolution of the basin. The subsurface basin geometry inferred from geophysical investigations is consistent with findings from surface geology.

The MAV is a Quaternary extensional basin whose post-orogenic polyphasic evolution was controlled by a conjugate, ~E-W and ~N-S striking fault system during the early stage of basin development and by a NW-striking fault system in a later phase.

During the Early Pleistocene the strike-slip conjugate system reactivated with oblique kinematics controlling the largest sedimentary traps, producing intra-basin bedrock highs and significant syn-tectonic deposition, and causing variable thickness and hiatuses of the continental infill.

Since the end of the Early Pleistocene, with the inception of the NW-striking fault system activity, several NW-strands linked into longer splays and their activity migrated toward a leading segment: the Paganica-San Demetrio fault alignment that exhibits maximum post-450 ka throw rate of 0.27 ± 0.07 mm/a.

Notably, two major elements of the ~E-W and ~N-S-striking faults act as transfer structures to the nearby stepping active fault systems or form the boundaries, as geometric complexities, that constrain the Paganica-San Demetrio fault system overall length to 19 ± 3 km. The resulting size of the leading fault segment is coherent with the extent of the 6 April 2009 L'Aquila earthquake causative fault.