Multiphase wavefield inversion methodology for seismic analysis of soil-structure interaction systems

Currently available inversion methods for providing seismic excitation for soil–structure interaction (SSI) systems regard all ground motions as the body wave component and invert only the body wavefields. However, the ground motions are dominated by body waves and surface waves, and ignorance of the latter has been demonstrated to be conservative for structural responses. To provide more accurate wavefields for the seismic input of SSI systems located on the half-space of rock mediums, a multiphase wavefield inversion (MPWI) methodology considering both body waves and Rayleigh surface waves is proposed in this study. The methodology applies forward modeling and inversion theory of body waves and Snell's law for complex angles to determine the exact Rayleigh wave components and construct the Rayleigh wavefields. The residual body waves are used to invert the body wavefields, focusing on optimizing the determination of incident angles by a least-squares iteration approach. Rayleigh and body wavefields are finally combined to construct the total wavefields. The efficiency of the proposed methodology is verified and validated with analytical solutions and real downhole recordings, and the applicability is examined by response comparisons with the traditional method in the free field and an urban complex building. Simulation results demonstrate that due to the consideration of the Rayleigh waves, the MPWI methodology results in higher free-field stresses and accordingly induces more intense seismic excitation. Correspondingly, the structural responses present an amplification effect.