The role of site effects in the comparison between code provisions and the near field strong motion of the Emilia 2012 earthquakes

Gallipoli M. R., Chiauzzi L., Stabile T. A., Mucciarelli M., Masi A., Lizza C., Vignola L.

Bulletin of Earthquake Engineering, 12(5) pp. 2211–2230, 2014 | doi: 10.1007/s10518-014-9628-7

ABSTRACT:

A damaging seismic sequence hit a wide area mainly located in the Emilia-Romagna region (Northern Italy) during 2012 with several events of local magnitude Ml ≥ 5, among which the Ml 5.9 May 20 and the Ml 5.8 May 29 were the main events. Thanks to the presence of a permanent accelerometric station very close to the epicentre and to the temporary installations performed in the aftermath of the first shock, a large number of strong motion recordings are available, on the basis of which, we compared the recorded signals with the values provided by the current Italian seismic regulations, and we observed several differences with respect to horizontal components when the simplified approach for site conditions (based on Vs30 classes) is used. On the contrary, when using the more accurate approach based on the local seismic response, we generally obtain a much better agreement, at least in the frequency range corresponding to a quarter wavelength comparable with the depth of the available subsoil data. Some unresolved questions still remain, such as the low frequency behaviour ( < 1 Hz) that could be due either to complex propagation at depth larger than the one presently investigated or to near source effects, and the behaviour of vertical spectra whose recorded/code difference is too large to be explained with the information currently available.