“…In DAS recordings obtained through cables on structures, the site characteristics differ from seismic instruments placed on the ground. Consequently, the differential phase of DAS measurement (∆Φ ni ( t )) while using the existing fiber cables along the railway with the seismic event n at channel # i is expressed as follows:
here, S n ( f ) is the source, P ni ( f ) is the propagation path, G i ( f ) is the site amplification on the ground, C i ( f ) is the coupling between the fiber cable and installation surface, R i ( f ) is the effect of amplification of the seismic wave by the railway structure, and O n ( f , θ ) is the orientation factor (Kennett,
2022; Kuvshinov,
2016; Martin et al.,
2018), which represents the effect of polarization and arrival direction on the seismic waveform.…”