Berlusconi, Andrea

In order to geometrically characterize the liquefaction features observed in the epicentral sector of the 2012 Emilia seismic sequence and to evaluate the potential for recording palaeoseismic features of the area, we performed two electric resistivity tomographic sections and 4 shallow corings, coupled with 14C datings and archaeological age estimates in selected sites. Preliminary results show that there is a good agreement between ERT sections and core-logs; moreover a major role in determining the scalar relationships of the liquefaction features is played by the local geomorphological and topographic setting. The high sedimentation rates obtained through core datings (4 – 20 mm/yr) suggest that the described methodological approach can cover time windows of only a few centuries, thus hardly encompassing, in this tectonic setting, a significant period for paleoseismological purposes.

We present high-resolution Vp models of the Middle Aterno basin obtained by multi-scale non-linear controlled-source tomography. Seismic data have been collected along four dense wide-aperture profiles, that run SW-NE for a total length of ~ 6 km in the hangingwall of the Paganica - S. Demetrio Fault, source of the 6th April 2009 (Mw 6.3) L'Aquila normal-faulting earthquake. Seismic tomography expands the knowledge of the basin with high spatial resolution and depth penetration (> 300 m), illuminating the Meso-Cenozoic substratum that corresponds to high-Vp regions (Vp > 3500-4000 m/s). Low Vp (1500-2000 m/s) lacustrine sediments (Early Pleistocene in age) are imaged only in the SW sector of the basin, where they are up to 200 m thick and lie below coarse fluvial and alluvial fan deposits. The overall infill consists of Early to Late Pleistocene alluvial fan and fluvial sediments between the Paganica Fault and the Bazzano ridge, with Vp reaching 3000 m/s for the oldest conglomeratic bodies. The substratum has an articulated topography. The main depocenter, ~ 350 m deep, is in the SW sector of the basin south of the Bazzano ridge. Remarkably, this depocenter and the overlying thick lacustrine body match the area of maximum coseismic subsidence observed after the 2009 earthquake. In the Paganica area, Vp images unravel large steps in the substratum related to two unreported SW-dipping buried strands, synthetic to the Paganica Fault, with ~ 250 m associated total vertical throw. This finding has important implications on the long-term history of the Paganica – S. Demetrio Fault system, whose total vertical displacement has been previously underestimated. An additional ~ 250 m vertical offset along this complex Quaternary extensional structure should therefore be considered.