Aggravation factors for 2D site effects in sedimentary basins: The case of Norcia, central Italy

In this article the seismic site response of the Norcia basin, Central Italy, has been analyzed using both 1D and 2D ground response numerical models. Period-dependent aggravation factors (PDAFs) quantifying the difference between 2D and 1D site response are provided for two representative cross-sections of the basin. Time-domain linear visco-elastic and non-linear analyses were carried out by the finite difference commercial program FLAC2D. For the former, the PDAFs were computed using a suite of representative ground motion records. Although the basin sediments are constituted by rather stiff soils, the Norcia basin is found to produce a consistent modification and enhancement of ground motion. It is found that the most important source of ground motion aggravation was the generation of Rayleigh waves at the basin edges. The variability of the PDAFs was explored by considering the effects of frequency content of input motion, damping ratio, irregularity of the alluvial-bedrock interface. The effect of the non-linear response of the sediments on the PDAFs was also addressed with reference to the Mw 5 October 30, 2016 event.