Reconstructing Urban Subsurface Structures by Using Metro Signals

Summary The background noise imaging method has been well applied in urban environments. In recent years, high-speed train vibration has become a new seismic source for subsurface exploration. The metro is similar to high-speed train with the advantages of food repeatability and wide distribution. And the metro is mainly distributed in cities, so it has great potential for urban underground imaging. Based on the characteristics of buried seismic sources, we derive a formula for the stationary phase zone of the metro. We deployed a linear array approximately perpendicular to a metro line in Wuhan. By stacking the results of different metro events, the clear Rayleigh surface can be extracted. The extracted Rayleigh waves are used to estimate S-wave velocity structure down to about 100 m depth.