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| | Abstract | | To evaluate the temporal change in the infrastructures, we have applied the time-lapse method. In road and/or embankment, the temporal change of physical properties affecting the life of constructions can be seen by seismic velocities change. We measured the time lapse of near-surface layer before and after the 23 mm rainfall in the test field. We used 100-m optical fibers and 4.5-Hz vertical geophones on the ground at every meter along 100-m line and a Mini-Vib with horizontal vibration. We ran the Mini-Vib every 30 min during daytime. The optical fibers were used as acoustic sensors as DAS. We compared two sets of waveforms, phases and travel times in a) both before the rain, b) both after the rain and c) before and after the rain. The direct comparison in each of a) and b) shows extremely small changes. The largest change was brought by precipitation. The before-and-after comparison revealed clear temporal change in waveforms, phases and travel times. The precipitation effects on body waves and Rayleigh wave were 1 ms faster at most and 15 ms (~1%) slower than ones before the rain, respectively. This discrepancy between body waves and surface wave can be explained by the different paths. |
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