Modelització analògica de l’efecte topogràfic: limitacions d’un estudi pilot i resultats

Abstract

The topographic effect causes seismic wave amplification on the top of the mountains. This amplification reportedly produces more damage on the infrastructures of these parts of the reliefs and for this reason this effect has been widely studied using mainly numerical and experimental approximations. However, it has never been studied using analogue modelling. This study aims to start pointing out the main issues and results of carrying out this type of modelling. Two gelatin analogue models have been made in order to achieve a correct scaling of crust’s elastic parameters and acoustic waves have been used in order to reproduce seismic Pwave propagation. Two experiments have been performed in the models allowing the observation of attenuation by geometrical spreading and topographic amplification in most of the acoustic signals. The experimental setup also affects the signals for some configurations producing anomalies in the attenuation and amplification tendencies. Measurements of the acceleration in the model’s surface have also been performed, but these don’t show any enhanced motions at the top of the relief. The amplification depends on the frequency of the acoustic waves, thus the waves with wavelengths more similar to the mountain’s length are the most amplified (12% to 28% of maximum amplification), which is in agreement with most of the studies. Nevertheless, the limitations of this study must be taken into account when it comes to relating the processes in the model with the natural ones. The absence of shear waves in the experimental runs and scaling problems, especially for the acoustic wave frequencies, constitute the main limitations of this study. However, the fact that some processes identified in the model actually occur in the nature, ensure the validity of the method at least from a qualitative perspective. Several improvements must be applied in this method in order to obtain better results and get more useful clues for the natural hazard assessment in the future.