A sostegno della mia tesi, posso citare il libro di Yoshida: 'Seismic Ground response analysis', Springer. Riporto tutto il paragrafo di interesse che descrive uno dei meccanismi dell'amplificazione sismica e allego la figura citata. In neretto sottolineato, il concetto che esclude che la base della struttura possa essere usata come superficie topografica.

Quote:
The earthquake waves propagated from engineering base layer are reflected when they reach the ground surface. Figure 1.6a schematically shows one period of a wave whose front just passes the ground surface. If there were no boundary, the incident wave (chained line) would propagate without any change as shown by a dotted line. Since the ground surface works as a free end, the wave is reflected
as mirror symmetry against the boundary as shown by the dashed line. Therefore composite wave (solid line), sum of the incident and reflected waves, becomes larger than the incident wave. The earthquake wave is amplified twice when it is reflected at the ground surface. Phases of the incident and reflected waves are identical at the ground surface, but phase lag occurs in the underlying layers. Therefore, amplification becomes smaller as it gets deeper.
Let us consider another example: if there is a structure on/in the ground, reflection that results in double amplitude does not occur. Therefore, the design that uses the earthquake wave at the free surface as the input motion for a structural analysis is not rational, because the earthquake wave at the ground surface is larger than the wave that hits to the structure. This is one of the reasons why soil–structure interaction is required to be considered in the structural design.



Immagini allegate
Yoshida fig 1.6.png (46.73 KB, 30 download)
"Data speak for themselves" -Reverend Thomas Bayes 1702-1761
P(Ai|E)=(P(E|Ai)P(Ai))/P(E)