The relation between macroseismic intensity and ground shaking makes it possible to transform instrumental Ground Motion Parameters (GMPs) in macroseismic intensity and vice versa, and is therefore useful for making comparisons between estimates of seismic hazard determined in terms of GMPs and macroseismic intensity, and for other engineering and seismological applications. Empirical relationships between macroseismic intensity and different recorded GMPs for the Italian territory are presented in this paper. The coefficients are calibrated using a dataset of horizontal geometrical mean GMPs, i.e. peak ground acceleration, peak ground velocity, spectral acceleration at 0.2, 0.3, 1.0 and 2.0 s from the ITalian ACcelerometric Archive (ITACA; Luzi et al. in Italian Accelerometric Archive v3.0, Istituto Nazionale di Geofisica e Vulcanologia, Dipartimento della Protezione Civile Nazionale, 2019.10.13127/itaca.3.0), and macroseismic intensity at Mercalli–Cancani–Sieberg (MCS) scale from the database DBMI15 (Locati et al. in Database Macrosismico Italiano (DBMI15), versione 2.0, Istituto Nazionale di Geofisica e Vulcanologia (INGV), 2019.10.13127/DBMI/DBMI15.2). A dataset is obtained that corresponds to 240 pairs of macroseismic intensity-GMPs from 67 Italian earthquakes in the time window 1972–2016 with moment magnitude ranging from 4.2 to 6.8 and macroseismic intensity in the range [2, 10–11]. The final dataset correlates strong motion stations and macroseismic intensity observations generally within 2 km from each other, and each association is manually validated through an expert judgement. The adopted functional form is non-linear, predicting macroseismic intensity as a function of LogGMPs and vice versa by performing separate regressions. The set of empirical conversion relationships GMP–I_MCS–GMP and the associated standard deviations are compared with previous models. In order to verify the proposed model, a map in terms of PGA is obtained, starting from the PSHA in terms of intensities (Gomez Capera et al. in Bull Seismol Soc Am 100(4):614–1631, 2010.10.1785/0120090212) and then using the empirical relationship here proposed in PGA, and compared with the National Italian seismic hazard map (Stucchi et al. in Bull Seismol Soc Am 101(4):1885–1911, 2011.10.1785/0120100130).

This study deals with the impact of deep-soil discontinuities on groundmotion amplification in the Po alluvial basin (northern Italy), and consequently, on long-period probabilistic seismic-hazard analysis estimates. The focus is on Castelleone, where a seismic station of the Italian National Seismic Network has been deployed since 2009. To define a detailed shear-wave velocity (VS) profile, extensive active and passive geophysical surveys were carried out. The active measurements included seismic profiles examined through standard refraction techniques and multichannel analysis of surface waves. The passive methods included ambient vibrationmeasurements in both single and array configurations. In particular, three microtremor arrays with increasing apertures were performed to capture the experimental dispersion curve down to 0.2 Hz. The horizontal- to-vertical spectral ratio (HVSR) showed two main peaks, at 0.17 and 0.70 Hz. A joint inversion of the experimental phase-velocity dispersion and HVSR curves was performed to obtain the VS profile. The data show two main discontinuities at ~160 and 1350 m in depth. According to the Italian and European seismic codes, the shallow VS discontinuity can be ascribed to the seismic bedrock (i.e., VS > 800 m=s), whereas the deeper one is observed at the transition between Pliocene-Quaternary deposits and Miocene marls. Preliminary site-specific seismic-hazard analysis in terms of displacement response spectra for periods up to 10 s shows that neglecting the effects of the deeper discontinuity implies underestimation in hazard estimates of up to about 49% for mean return period (MRP) of 475 years and about 57% for MRP of 2475 years, with possible consequences regarding the design of very tall buildings and large bridges