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The additional information about the two earthquakes
provided by IAEE Director Prof. Ezio Faccioli.
Salient aspects of the impact to the built and natural environment include:
1. The collapse of, or heavy damage to, industrial buildings, mostly prefabricated shed structures, in a number of cases lacking displacement capacity between the top of the columns and the beams ends resting on them. Because of these collapses, the majority of the dead were industrial workers (on their night shift for the first earthquake or - in the second earthquake - back to work in structures that were unsafe after the first event, and had not been properly diagnosed). The epicentral area, especially for the second event, coincides with a densely industrialized district, with vocation for precision mechanics and biomedical apparel: hundreds of firms, small and large, were directly affected. As to the role of seismic codes, only for structures built after 2003 was the design for earthquake resistance compulsory, with 10% in 50 yr probability PGA of 0.12 - 0.15 g. For the observed severity of the shaking, I attach two pdf tables summarizing the values of peak ground motion parameters for both the first and second event (PDF1, PDF2). Note that in the first one, the largest PGA of 0.3g was recorded at some 13 km epicentral distance (station MRN). In the second event, the same MRN station recorded much closer to the source (4 km) with roughly the same PGA.
2. Damage to monumental structures of historical and architectural value, especially castles of the late Middle Age, of which you have all seen many pictures in the media. It will take time to assess properly the real extent of this damage and these losses.
3. Extensive impact of liquefaction and lateral spreading affecting, in many cases, surficial layers of silty sands; I attach just one picture as a representative example (from the first event). These effects were especially pervasive in some places, like the hamlet of San Carlo, close to the commune of San Agostino (Modena province). Never was liquefaction observed so extensively in Italian earthquakes since many decades.
4. The picture of the faults whose rupture generated the earthquakes, beyond the fact that they were pure E_W oriented thrusts compatible with regional tectonics, is complicated: all the faults occur under 3 to 7 km of sedimentary layers and come in complex fault systems which the INGV fault database classifies as "composite sources", assumed to be capable of Mmax = 5.9. A similar sequence of earthquakes was observed (and well documented) for the last time in this region (Ferrara) in 1570 A D.
It would be well to tell viewers that a clearinghouse has been established at the Emilia Earthquake clearinghouse by EERI and Eucentre. This provides various other links to other sources.