GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 2.1 178 In the following we summarize the results of the analysis. Due to the scarcity of the seismic stations, it is not possible to develop a reasonable interpretation of the impulsive motions in Friuli (IT-1976-0025, IT-1976-0027, IT-1976-0030) and Irpinia earthquakes (IT-1980-0012). Starting from the L’Aquila earthquake (IT-2009-0009), we are able to retrieve more specific information about the impulsive signals and their relations with earthquake physics and soil conditions. During the L’Aquila earthquake sequence, the stations that recorded impulsive motions were located on top of the fault plane. Two of these impulsive stations are AQK and AQV, with site amplifications around 0.6 Hz (D’Amico et al., 2020). Furthermore, these stations are close to each other, and they all have a B soil class (Luzi et al., 2016). Periods of impulsive signals vary between 0.9 s to 1.7 s depending on the station (Ertuncay et al., 2021). A qualitative analysis of the impulsive horizontal ground motions in the four stations that recorded impulsive signals shows that horizontal displacements substantially differ from each other (Figure 1), although stations are within about ten kilometers. Emilia earthquake sequence (IT-2012-0008, IT-2012-0010, IT-2012-0011, IT-2012-0012) created a larger number of impulsive signals than L’Aquila, also because of the temporary installation of additional seismic stations in the near-field area after the first shock. During the 9th of May 2012 (07:00) Emilia earthquake, seismic stations recorded various impulsive signals that show similar displacement patterns in horizontal axes, which are also in correlation with the slip distribution of the fault plane (Figure 2). Motions of the stations are dominated by the North- South movement, which is similar to the slip distribution and the 90-degree rake angle. Fig. 1 - Plot of the horizontal displacements of stations AQG, AQV, AQU, and AQK that are labelled as impulsive in the 2009 L’Aquila earthquake. Fig. 2 - a) Particle motions of stations with impulsive signals on 29th of May 2012 (07:00) Emilia-Romagna earthquake (Ertuncay et al., 2021), and b) slip distribution of the earthquake (Paolucci, R. et al., 2015).