Numerical investigation of influence of near-surface lateral heterogeneities on propagation of Rayleigh waves

Abstract

Recent research on earthquake disasters has provided evidence that Rayleigh waves play a crucial role in causing damage to both underground and surface structures during earthquakes. In this study, we utilize the finite difference method to investigate the impact of the interaction between Rayleigh waves and near-surface heterogeneities on seismic ground response. Specifically, we analyze the effects of different types of cavities (vacuum cavity, water-filled cavity, and soft-soil-filled cavity) as well as granite boulders on the propagation of Rayleigh waves. Furthermore, we examine how the buried depth and size of the heterogeneous structure, as well as the distance from the center of the structure, influence the amplitude and frequency spectrum of Rayleigh waves. Our numerical results reveal that the presence of cavities leads to larger amplitudes of Rayleigh waves compared to the free field, with the amplification effects becoming more pronounced as the cavities become shallower. Although the amplitude of Rayleigh waves generally decreases with increasing offset, the complex interaction between Rayleigh waves and the heterogeneous structure causes significantly smaller amplitudes on the far offset side of the cavity, while the near offset side exhibits significant amplification phenomena. Moreover, the characteristics of the Rayleigh-waves field vary depending on the filling material inside the cavities. For instance, the wall of a water-filled cavity clearly shows the presence of Scholte waves, whereas a soft-soil-filled cavity exhibits an energy traps phenomenon. Additionally, the conversion phenomena of Rayleigh waves generated by these two types of cavities are characterized by strong energy and smooth continuity. On the other hand, granite boulders have a relatively minor influence on Rayleigh wave propagation at the far-source side, except for partial scattering of waves. However, at the near-source side, significant amplitude amplification occurs in the vicinity of granite boulders, particularly for the high-frequency radial component. Therefore, considering the intricate interaction between Rayleigh waves and near-surface lateral heterogeneities, the findings of this study can serve as valuable guidance for seismic micro-zonation and the design of observation systems using the high-frequency surface-wave method.