Investigating Rupture Direction for Three 2012 Moderate Earthquakes in Northern Italy from Inversion of Peak-Ground Motion Parameters

We investigate the possibility of inferring the dominant horizontal rupture direction for moderate earthquakes from the inversion of peak-ground motion parameters. To this aim, we adopt a technique which was devised and applied to large earthquakes for retrieving both the dominant rupture direction and the surface fault projection, to be used, with a proper distance metric, to refine ShakeMaps® computation. In the present paper, the procedure was applied to three moderate earthquakes occurred in Northern Italy three days apart, i.e., the 2012/01/24, M 4.2, Pre-Alpi Venete earthquake, the 2012/01/25, M 4.9, Reggio Emilia earthquake, and the 2012/01/27, M 5.4, Parma earthquake. For two of the three analyzed events, the technique identifies a dominant horizontal rupture direction which is consistent with the strike directions inferred from the focal mechanisms. For the M 5.4 event, which is a deep (about 61km) thrust-faulting mechanism earthquake, the inferred dominant rupture direction allows to identify the north-east-dipping plane as the fault plane in accordance with the aftershocks distribution.