On May 20th, 2012, at 02:03 UTC (04:03 local time), Emilia region of Northern Italy was struck by an earthquake of local magnitude ML 5.9. The focal mechanism was reverse, with maximum compression along the N–S direction (dip = 46.45âˆ˜, strike = 103.28âˆ˜, rake = 93.87âˆ˜). The municipalities that suffered the highest damage were San Felice sul Panaro and Finale Emilia. Many other damaged municipalities were located in the districts of Modena and Ferrara. The main shock was preceded by foreshocks, begun on May 18th, the strongest of which, with local magnitude 4.1, occurred on May 19th at 23:13 UTC. After the main shock, several aftershocks occurred. At 23:00 of May 25th, more than 500 events took place, two of which with ML≥ 5.0 (event of May 20th, 13:18 UTC, ML 5.1; event of May 25th, 02:07 UTC, ML 5.1), and 15 with magnitude ranging between 4.0 and 4.9 (INGV 2012).
On May 29th, at 07:00 UTC, another significant event of magnitude ML 5.8 occurred, located nearly 12 km W of the May 20th main event and close to San Felice sul Panaro. This event was followed by two aftershocks of ML≥5.0. The aftershocks of the May 29th events affected an area elongated according to the E–W direction, between the municipalities of Novi di Modena and San Felice sul Panaro, nearly 20 km long. On June 3rd, a new event of magnitude ML 5.1, located to the W of the previous ones struck the same area (INGV 2012).
The maximum macroseismic intensity, measured according to the European Macroseismic Scale (IEMS), was VIII in the municipality of Cavezzo as the cumulative effect of the sequence (Tertulliani et al. 2012). In the most damaged municipalities (IEMS>VII), a few total collapses were observed. Collapses of individual reinforced-concrete (RC) buildings occurred in the municipalities of San Felice sul Panaro and Finale Emilia, as well as severe damage to monumental buildings and to old constructions.
For the May 20th event the maximum horizontal ground acceleration recorded in the epicentral area was 0.26 g and the maximum vertical ground acceleration 0.31 g. For the May 29th event the maximum horizontal ground acceleration was 0.31 g and the maximum vertical ground acceleration an impressive 0.87 g.