Effects of P-Wave and S-Wave Impedance Contrast on the Characteristics of Basin Transduced Rayleigh Waves

Abstract

Different aspects of body wave amplifications in a basin have been studied in detail in the past. However, the study on amplification of basin-transduced surface waves is very limited, although surface waves are more damaging as compared to body waves. This paper presents the effects of P-wave and S-wave impedance contrast (IC) at the basin-edge on the spectral amplification and complex mode transformation of basin-transduced Rayleigh (BTR) waves. BTR-waves, the acronym for basin-transduced Rayleigh waves, is used in the manuscript. Analysis of simulated results reveals a complex mode transformation of Rayleigh wave after entering the basin. The less dispersed horizontally polarised first mode and highly dispersed vertically polarised fundamental mode of BTR-waves were inferred in the basin. The first mode of BTR-waves is developed in a frequency bandwidth and the frequency content in that is very much dependent on the Poisson’s ratio and fundamental frequency of soil in the basin. An increase of phase velocity of first mode of BTR-waves with Poisson’s ratio is obtained. It is concluded that spectral amplification of BTR-waves depends on both the P-wave IC and S-wave IC at the basin-edge. An increase of the largest and average spectral amplifications of the horizontal component of the BTR-wave is obtained with the increase of both the P-wave IC and S-wave IC. On the other hand, an increase of the largest and average spectral amplification of the vertical component of the BTR-wave is obtained with the increase of P-wave IC, but such a systematic and significant effect is not inferred with the increase of S-wave IC at the basin-edge.