Analysis of Depth Spatial Variations of Accelerograms Recorded from the Center for Engineering Strong Motion Data: Numerical Simulation for Multipoint Ground Motions

Studies on depth spatial variations are rare because of the limited number of measured recordings of the subsurface along the depth direction from the ground surface. However, these depth variations can directly influence the seismic dynamic response of underground structures or the foundations of space structures through multi-support excitation. In this study, depth spatial variations, including phase and amplitude, are analyzed to describe ground motions along different depths based on surface-earthquake time histories. The observed recordings from the Center for Engineering Strong Motion Data are used to investigate the spatial variation characteristics of the phase and amplitude in the depth direction, represented by the lagged coherence and Fourier amplitude spectrum ratio, respectively. A corresponding model is established under various site conditions to simulate multipoint correlated ground motions along the depth from the surface. Finally, a numerical simulation of multipoint ground motions is conducted to verify the application of the established models. This study provides an effective tool for describing spatial variations in both phase and amplitude, which are crucial for simulating ground motions at various depths.