Seismic site amplification induced by topographic irregularity: Results of a numerical analysis on 2D synthetic models

This study concerns the evaluation of seismic site effects and their relation to the local topographical characteristics of a slope. The seismic amplification (SA) on the free surface is calculated by a numerical model using the finite elements (FE) method. Synthetic models by utilized in the FE analysis represent a slope with an inclination ranging from 10° to 41°. At the crest and valley of the slope the models were considered horizontal and indefinite. The site effects were calculated on the free surface in several nodal points. The input motion used in the analysis was a SV seismic wave with variable frequency between 0.5 and 32 Hz. The seismic site analysis confirmed that in absence of sediments, ground motion is more amplified at the upper slope break than in other points of the model. In regard to seismic amplification vs. the frequency we can affirm that seismic amplification reaches its maxima in the band 4-16 Hz and with slope angle value computed at the highest degree. It is also clear that a nonlinear seismic amplification response in the crest and valley zone while SA would seem to have a linear response in other zones. We propose an empirical method to estimate the SA in the regular slope far from the crest and valley zone.