Evaluation of topographic aggravation factors through 2D equivalent linear seismic response analysis

Evidence of past earthquakes showed that topographic irregularities affect the seismic site response and in many cases are responsible for large amplifications of the seismic motion and consequently of damages to structures and lifelines. In this paper the seismic response of simple slope geometries under vertically propagating SV waves is investigated through two-dimensional FE numerical analyses with the aim of evaluating the topographic aggravation factor. The analyses were performed using the finite element code QUAKE/W (Krahn, 2004) considering a finite height slope overlying a linear elastic bedrock and assuming that under seismic loading soil behaves as a linear or equivalent linear. The results of the linear visco-elastic analyses show that the presence of a compliant bedrock does not significantly affect the topographic amplification: conversely the equivalent-linear analysis results highlight the significant dependence of the topographic aggravation factors on the non linear soil behavior; specifically, for particular values of the frequency of the input motion, the topographic aggravation factors result larger than those obtained through linear visco-elastic analyses.