GNGTS 2015 - Atti del 34° Convegno Nazionale

Fig. 2 – Results of the 1D and 2D numerical modeling (top and middle) and the geological cross-section considered (vertical exaggeration). With the black line is indicated the position of the seismic bedrock. Contour maps of the maximum shear strain: a) 2D heterogeneous model; b) 2D homogeneous model; c) 1D heterogeneous model; d) 1D homogeneous model. 180 GNGTS 2015 S essione 2.2 as a vertically incident SV-wave at the model bottom. The amplification function distribution, A( f ) x , was computed along the numerical domain, as ratio in the frequency domain between the motions calculated on the sediments and the reference outcropping bedrock motion at the location of the volcanic deposits (Fig. 1). The numerical domain is characterized by specific lateral heterogeneous absorbing layer systems. For the modeling a perfectly elastic rheology were assumed so estimating the maximum expected displacements at the valley surface. Other simulations are actually ongoing by considering a visco-elastic rheology. The model was discretized considering a triangular mesh with linear interpolation, the size of the elements was chosen according to the minimum inter-nodal distance respect Eq. 1: (1) with λ = wavelength and Δ h = minimum inter-nodal distance. Considering the value of 118 m/s as the lowest S-wave velocity (Vs) characterizing the alluvial deposits and the corresponding value of 1100 m/s for the seismic bedrock , the minimum inter-nodal distances retained are of 1 m and of 10 m for the deposits and for the seismic bedrock respectively. These inter-nodal distances ensure a frequency resolution up to 10 Hz. The model is composed by 269,917 nodes each with 2 degrees of freedom. The obtained results were analyzed in terms of wave propagation, amplification functions and ground-shaking energy along the considered profile (Fig. 2). The resulting A( f ) x were interpolated through a Kriging method to obtain a representation along the section as function of the frequency. λ