Elastic Wave Equation Traveltime Inversion With Dynamic Time Warping Based on High-Speed Train Seismic Data

The high-speed train (HST), as a special kind of seismic source, can be simplified as a mobile combination source. The HST-induced seismic data (also known as HST seismic data) contains rich geological structural information. However, HST seismic data interfere highly in space and time and their spectra have narrow-band separation spectral characteristics in frequency domain. It is very difficult to effectively extract the geological structural information contained in HST seismic data. In this work, we try to use the elastic wave equation traveltime inversion (EWTI) method to explore the subsurface velocity information using the seismic data induced by HSTs running on viaducts, which is conducive to providing a more reliable initial model to serve full waveform inversion (FWI). However, as mentioned previously, HST seismic data are highly complex, which makes the EWTI method based on first-break picking no longer applicable to them. Therefore, we apply dynamic time warping (DTW) to obtain the time shifts between observed HST-induced seismic data and synthetic HST-induced seismic data. Based on the time shifts obtained by DTW, the subsurface velocity model can be updated by establishing the misfit function and calculating the gradient. Numerical experiments using the simple velocity anomaly model and the Marmousi2 model show that the DTW-based EWTI method is able to obtain the large-scale background model and provide a reliable initial model to serve FWI. The results in this work also demonstrate the considerable potential of underground exploration using HST-induced seismic data.