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 horizontalrupture
direction for moderate earthquakes from the inversion of peak ground-motion
parameters. To this aim, we adopt a technique that 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 the ShakeMap computation.
In the present paper, the procedure was applied to three moderate earthquakes
that occurred in 2012 in Northern Italy three days apart: the M 4.2 Pre-Alpi Venete
earthquake on 24 January, the M 4.9 Reggio Emilia earthquake on 25 January, and the
M 5.4 Parma earthquake on 27 January. 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 theM 5.4 event, which is
a deep (about 61 km) thrust-faulting mechanism earthquake, the inferred dominant
rupture direction allows identification of the northeast-dipping plane as the fault plane in accordance with the aftershocks distribution.