Investigating the architecture of the Paganica Fault (2009Mw6.1 earthquake, central Italy) by integrating high-resolution multiscale refraction tomography and detailed geological mapping

We present a 2-D subsurface image of the Paganica Fault from a high-resolution refraction
tomography and detailed geological investigation carried out across part of the northwestern
segment of the 20-km-long Paganica–San Demetrio fault-system, and which was responsible
of the 2009 April 6 Mw 6.1 L’Aquila earthquake (central Italy). We acquired two seismic
profiles crossing the Paganica basin with a dense-wide aperture configuration. More than
30 000 P wave first-arrival traveltimes were input to a non-linear tomographic inversion. The
obtained 250–300 m deep 2-D Vp images illuminate the shallow portion of the Paganica
Fault, and depict additional unreported splays defining a complex half-graben structure. We
interpret local thickening of low-Vp (<2400 m s−1) and intermediate-Vp (2600–3400 m s−1)
regions as syn-tectonic clasticwedges above a high-Vp (3800–5000ms−1) carbonate basement.
These results are condensed in a 4.2-km-long section across the Paganica basin, clearly
indicating that the Paganica Fault is a mature normal fault cutting the whole upper ∼10 km
of the crust. We evaluate a minimum cumulative net displacement of 650 ± 90 m and a total
heave of 530 ± 65 m accomplished by the Paganica Fault, respectively. In the conservative
hypothesis that the extension started during the Gelasian (1.80–2.59 Ma),we obtain a minimum
long-term slip-rate of 0.30 ± 0.07 mm yr−1 and an extension-rate of 0.25 ± 0.06 mm yr−1,
respectively. Considering the regional averaged extensional field of ∼1 mm yr−1 obtained
from geodetic and geological analyses at 104 yr timescale, we infer that the Paganica Fault
accounts for ∼20 per cent of the NE-extension affecting this zone of the central Apennines
axis due to the concurrent activity of other parallel normal fault-systems nearby (e.g. the Liri,
Velino-Magnola, L’Aquila-Celano and Gran Sasso fault-systems).

This article has been accepted for publication in Geophysical Journal Internationa ©: 2017 Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.