Parametric numerical study of observed amplification effects on the colle di roio limestone ridge (Central italy)

Following the seismic microzonation studies of the L’Aquila area, Central Italy, hit by the Mw 6.3 L’Aquila earthquake of 6th April 2009, we observed ground motion amplification at the hilltop of the Colle di Roio limestone ridge. In particular, horizontal-to-vertical spectral ratio amplitude of weak motion waveforms showed average peak level above 5 in the frequency range 4-5 Hz. In order to evaluate the contribution of topography and subsoil heterogeneity on the observed response, we performed 2D numerical simulations of wave propagation through the ridge using a finite difference approach. Different hypothesis of model configuration, consistent with the available geological data, were tested. A homogeneous model was considered to evaluate the effect of surface topography on ground motion amplification, while several heterogeneous models were considered in order to examine the interaction between topography and heterogeneity on the seismic response. Results were analyzed in terms of synthetic horizontal-to-vertical (H/V) spectral ratios and the latter were compared to the observed ones. The results showed that the observed ground motion amplification level cannot be explained only by surface topography effect and that the assumption of an heterogeneous model with complex inner geometry may fairly reproduce the observations. © Springer International Publishing Switzerland 2015.