Theoretical analysis of high-speed rail seismic imaging

We do theoretical research on using high-speed rail(HSR)as an active source to perform reverse time migration(RTM)and analyze the influence of the interferometric field on the seismic imaging results.When a train runs on a rail viaduct,the evenly spaced piers of the viaduct generate a nearly spherical interferometric wavefield with radically travelling waves in frequency-determined directions.We find that the directions span stationary areas of the interference phases,of which cross-talks deteriorating HSR seismic imaging can be well suppressed by stacking.Accordingly,we propose a method for performing RTM by employing HSR data.Numerical tests primarily verify the proposed method by use of 2 D and 3 D acoustic wave equations.Subsequently,we execute least square RTM to suppress crosstalk artifacts,further improving the imaging quality.At last,we stack images derived from trains with different velocities,which extends the frequency band,effectively overcoming the limit from the discrete spectrum of the source wavelet.