Investigating the architecture of the Paganica Fault (2009 Mw 6.1 earthquake, central Italy) by integrating high-resolution multi-scale refraction tomography and detailed geological mapping. Issue 2 (2nd November 2016) - Villani, F.
Abstract: 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 north-western segment of the 20 km-long Paganica – San Demetrio fault-system, and which was responsible of the 6 April 2009 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 clastic wedges above a high- Vp (3800-5000 m s −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 geologic analyses at 10 4 yr timescale, we infer that the Paganica Fault accounts for ∼ 20% 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).