MAY 2012 EMILIA EARTHQUAKES (MW 6, NORTHERN ITALY): MACROSEISMIC EFFECTS DISTRIBUTION AND SEISMOTECTONIC IMPLICATIONS

Abstract

We have carried out the macroseismic survey of both the May 20 (Mw 6.1) and May 29 (Mw 6.0) earthquakes in Emilia (Po Plain, northern Italy) by applying the Mercalli-Cancani-Sieberg scale, on 190 localities, mainly spread south of the Po River. Our data account for an Io 7 MCS evaluated for both earthquakes, with an Imax 7-8 assigned to the village of Rovereto after the mainshock of May 29. Damages were mainly focused on the historical buildings of the region, such as churches, castles, and towers, beside on the industrial warehouses, the collapse of which caused most of the victims of the two mainshocks. Churches and bell-towers were hit also in villages located far from the mesoseismic area, resulting often the only buildings affected by the earthquake. The seismic shaking induced also hundred of liquefaction phenomena that, in some places, have increased the damage level to buildings. By comparing macroseismic and instrumental data (i.e., hypocentres distribution, focal mechanisms, interferograms), to the deep geological structures of the region, it emerges that the May 20 mainshock was caused by a segment of the outer Ferrara thrusts front, whereas the May 29 mainshock by the Mirandola thrust. As these thrusts have been seismically silent in the past millennium, the current sequence fills partially a seismic gap along the seismogenetic structures of the buried outer Apenninic front.