GNGTS 2014 - Atti del 33° Convegno Nazionale

244 GNGTS 2014 S essione 2.2 Conclusions. An important feature that arises from the analysis of HVSR curves obtained in the study area, is the widespread presence of seismic resonance phenomena in the range (0.8 – 1.3 Hz). This could be responsible for seismic amplification effects that could trigger damages of large dimension structure like industrial warehouse, as observed in occasion of the May-June 2012 seismic sequence. From the geological point of view, the main resonant interface is possibly related with a sub-horizontal unconformity at depth in the range 55-110 m. This interface is located within the Quaternary continental alluvial sequence, between two sedimentary cycles of Middle Pleistocene: the Bazzano Subsynthem and the Undifferentiated Emiliano-Romagnolo Upper Synthem. A further deeper resonant interface (with depth of the order of several hundreds of meters) is also revealed by the presence of a low frequency HVSR peak (in the range 0.25- 0.3 Hz) possibly corresponding to the contact between whole Quaternary alluvial succession and Quaternary marine succession (Lower Pleistocene). In the Mirandola zone, these resonant surfaces coincide, due the rising of the Pliocenic geological substratum caused by the presence of the buried thrusts and folds ridge: this can explain the sharpness of the single HVSRmaximum detected in this area. Two other important outcomes of this work are: Fig. 3 – ������� Average V S profile up to a depth h relating to whole study area. Colored curves are concerned to S V ( h ) profiles obtained by borehole seismic tests and black lines are S V ( h ) profiles obtained by dispersion curves; red lines are minimum ( V 0 = 55, x = 0.43) and maximum ( V 0 = 120, x = 0.3) power law taken in account to assess the model variability.