GNGTS 2022 - Atti del 40° Convegno Nazionale

198 GNGTS 2022 Sessione 2.1 of the acceleration response spectra atT=0.07-0.4s). Furthermore, we take into account the spatial distribution and the focal mechanisms of shallow crustal earthquakes since 1985 and the seismogenic faults of DISS. The proposal of zonation for source correction is finally shown in Figure 1. The areas in which the GMM for active crustal earthquakes can be applied are 21, but those in which it is actually possible to estimate corrective factors are only 17, because of the scarcity of recorded data; in addition, the ITA18 model cannot be applied to areas in which seismicity is caused by volcanic activity (flagged with number 100). We find that the areas in which the average seismic motion of ITA18 is affected by a median δB e > 0.2 (natural log units), are located in northern Italy, in the Alpine chain (Western and Northern Alps, zones 1 and 2) and, remarkably, in the south, i.e., in the Apulian Foreland (13) and in the Western Lobe of the Ionian fault (16). In the latter cases, the mean observed seismic motion is 1.52 and 1.66 times higher than the median GMM prediction for zone 13 and 16, respectively. On the contrary, the areas, where the predicted ground motion overestimates the observations are found in southern Italy, i.e. the Molise region (12), Northern Sicily (19) and the Eastern Lobe of the Ionian Fault (14); the observed decrease in amplitude of ground motion is about 30% in zone 19. In the other cases the deviation from the reference model is within +/- 20%.   Fig. 1 - Zonation for regionalization of source effects (δB e ) into GMMs.