GNGTS 2021 - Atti del 39° Convegno Nazionale

179 GNGTS 2021 S essione 2.1 Central Italy earthquakes were also characterized by many impulsive signals, and also in this case, the installation of temporary stations allowed to acquire a larger amount of impulses. Most of the impulses were recorded during the 30th of October 2016 earthquake (EMSC- 20161030_0000029), and they occurred almost along all directions (fault normal, fault parallel and vertical). The three algorithms used for the identification of the impulses identified impulsive signals with various periods in which the largest period is calculated as 7.2 s (Figure 3). Impulsive signals are located on the Southern side of the ruptured area in which the fling step effect is observed (D’Amico et al., 2019). The analysis of the impulses recorded in earthquakes in Italy raises some preliminary evidence-based considerations about the potential influence of site effects on impulsive signals, focusing mainly on the horizontal component, and indicates the path towards new researches. Starting from L’Aquila records (6th of April 2009, 01:32:40), it is possible to observe that local site effects could have played an important role in the variation of the ground motion impulsive signal. This can be also recognized when looking at horizontal displacements of impulsive signals in the 30th of October 2016 (06:40:18) earthquake (see Ertuncay et al., 2021, for a more detailed description), where also very closed stations show horizontal displacement plots with sensible differences. Conversely, in the 29th of May 2012 (07:00) earthquake in Emilia-Romagna, the plot of the horizontal particle motion shows a similar pattern for all those stations that are positioned from North to South and are in perpendicular alignment with the maximum slip of the earthquake. These observations highlight the need to further study the effects of local site conditions on impulsive signals, with in-depth and focused analyses. Moreover, the analysis of impulsive signals shows that, under specific conditions, impulsive signals can be present also in the vertical component of the seismic ground motion. Vertical and horizontal impulses should be further studied also to investigate deeply their potential effects on the built environment, especially when considering friction-based structures, including stone masonry buildings, that still characterize a large part of the built environment in historical city centers in Italy. Fig. 3 - Particle motions and displacement-time histories of T1214 stations recorded during the 30th of October 2016, Norcia earthquake (Ertuncay et al., 2021).