This electronic supplement includes a table, seven figures, and a movie. Table S1 provides detailed information of the 21 train-related long-period long-duration (LPLD) signals. Figure S1 shows waveforms and spectrograms of more LPLD signals on both broadband and nodal stations, as well as a known train signal recorded by another station not used in this study. Figure S2 is frequency–wavenumber (f-k) amplitude (beam power) contours for reader to further evaluate the results of beamforming analysis. Figure S3 denotes relative energy recorded by all the nodal stations across the array for two LPLD events. Figure S4 demonstrates that moving source will not affect the decay rates with distance from the railway. Figures S5–S7 are daily mean local similarity trace for the whole study period, with the identified train-related LPLD signals highlighted. Movie S1 is a sonification of seismogram recorded at station YW.508 showing the harmonic nature of the train related signals.
Table S1. Detailed information of the detected train signals.
Figure S1. Additional examples of possible train-generated seismic signals. (a) Same event as in Figure 3 recorded by a nodal station 1001; (b) an event on 27 June 2016 recorded at the broadband station 508; (c) an event on 29 June 2016 recorded by the broadband station 508; (d) train-generated seismic signals recorded at station A002 within 3 km of another railway in Morrison, Oklahoma.
Figure S2. The contour plot denoting the distribution of f-k amplitude (beam power) as a function of back azimuth (angle) and wavenumber (radius) for different time windows.
Figure S3. Calculated energy across the array for LPLD events on (a) 29 June 2016, 06:00–07:00 and (b) 27 June 2016, 07:00–08:00.
Figure S4. Decay of cumulative energy in different 120 s windows from 22,320 to 22,680 s, with overlap of 60 s.
Figure S5. Daily mean local similarity trace from 22 June 2016 to 29 June 2016. The visually identified train signals are marked by red boxes.
Figure S6. Daily mean local similarity trace from 30 June 2016 to 7 July 2016.
Figure S7. Daily mean local similarity trace from 8 July 2016 to 17 July 2016.
Download: Movie S1 [h.264-encoded MPEG-4 video; ~518 KB]. The earthquake sound of the same event in Figure 3 in the main article.
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