Effects of impedance ratio between basin sediment and surrounding rock on seismic ground motions and basin-induced Rayleigh waves

A method for extracting Rayleigh wave phases from simulated seismograms is proposed by incorporating the F-K filtering and polarization analysis based on the time-frequency S transform. Then the effects of impedance ratio (IC) between basin sediment and surrounding rock on the basin ground motion and basin-induced surface wave are investigated. The results show that: (1) The Rayleigh waves can be satisfactorily identified and extracted by using this method. (2) The amplification effects of the basin are significantly affected by IC. The maximum amplification factor (AF_max) of the horizontal component increases with growing IC, with a largest value of about 1.15 for the studied cases. Contrastly, AF_max of the vertical component decreases with larger IC with the largest value of 0.85. In addition, horizontal ground motion at basin slope region is gradually weakened with reduced IC. (3) IC has obvious influences on the distribution features of intensely amplified regions of the basin. Under small IC, a few such regions occur in the basin, however, under large IC, these regions only appear at the basin edge. (4) With increasing IC, the amplitude of the basin-induced Rayleigh waves becomes lower, but the duration gets longer, and their travelling speeds become larger. (5) For the small IC case, an obvious oscillation of the surface wave amplitude (SWA) is observed, whereas for large IC model, the largest SWA only appears near the basin edge, and it is almost unchanged inside the basin. (6) The ratio of SWA to PGD decreases with the growing IC for the horizontal component, and the largest ratio occurs at the basin edge. However, this ratio is insensitive to IC for the vertical component, and it generally increases with larger distance from the basin edge.