Wavefield Modeling and Characteristic Analysis for a Uniformly Moving High-Speed-Train Source Under a Two-Layered Model With Applications

High-speed train (HST) seismology has emerged recently, which regards the HST as a repeatable moving seismic source. To make full use of the HST source for the detection and monitoring of near-surface geological structures and physical properties, the wavefield modeling for the HST source is crucial to deeply understand and illustrate the wavefield characteristics of the HST source. In this article, we simplify the near-surface as a two-layered model and treat the HST as a moving combination source with uniform velocity, containing a series of moving subsources (single wheel). Using the principle of superposition, we derive the semianalytical formula of the HST wavefield for a two-layered model. By computing the synthetic seismograms, the multidomain characteristics of the HST wavefield are comprehensively analyzed. Furthermore, we illustrate the wavefield energy distribution of HSTs with the different moving velocities. When the moving velocity of the HST source exceeds the Rayleigh-wave velocity, the response in the direction perpendicular to the railway exhibits the slower decay and higher amplitude. To integrate with the practical applications, we make a similarity comparison between the synthetic data and the field data. The results of the two-layered model show good agreement with the field data in both time and frequency domains. In particular, we evaluate the detection capability of HST vibration signals received at distances away from the railway up to a few kilometers. These conclusions will contribute to the practical applications of the HST source in seismic imaging and monitoring of geological conditions around high-speed railways.