Active and passive surface-wave recordings along high-speed lines

Seismic uniform linear arrays (ULAs) with a length of 23.75 m and composed by 96 geophones spaced at intervals of 25 cm were installed in 3 different sites (sites 1, 2 and 3). The ULAs were positioned on the cess (i.e. the track side) along the railway, at approximately 2 m from the rails, on track 1 for site 1 and track 2 for sites 2 and 3. Active seismic data was acquired by vertically striking a metal plate placed in-line, 12.5 cm away from the first (direct shot) and last (inverse shot) geophones.The impact was achieved with a hammer (1.5 kg) and waves propagation along the ULA was recorded for 2 s with a sampling interval of 0.5 ms (i.e. sampling rate of 2 kHz) and a pre-triggering delay of -0.02 s. Six direct and inverse shots were stacked in the time domain to enhance signal-to-noise ratio.HST passages on tracks 1 and 2 were also recorded with the exact same ULAs for durations of 120 s with a sampling interval of 2 ms (i.e. sampling rate of 500 Hz). The recordings were initiated manually upon visual confirmation of approaching trains at the site.