News Finding: It could be fluctuations in groundwater levels, or changes that could provide early warnings for a variety of geohazards such as permafrost thaw, sinkhole formation, and landslides."
Paper Finding: According to values reported in literature, the 2% limit could easily be exceeded by a variety of near-surface V S changes caused by processes such as water content variations (up to 10-15% ) and freeze-thaw transitions of unconsolidated permafrost (up to 70-80% ).
News Context: Added Dou: "We can monitor the near surface really well by using nothing but traffic noise. It could be fluctuations in groundwater levels, or changes that could provide early warnings for a variety of geohazards such as permafrost thaw, sinkhole formation, and landslides." In all cases, DAS proved to be comparably sensitive to earthquakes as conventional seismometers, despite its higher noise levels.
Paper Context: Although the resolvable depth ranges will be site-specific (depending on the local ambient-noise source field), we expect comparable time-lapse repeatability levels for the well-constrained portions of V S profiles at other locations. According to values reported in literature, the 2% limit could easily be exceeded by a variety of near-surface V S changes caused by processes such as water content variations (up to 10-15% ) and freeze-thaw transitions of unconsolidated permafrost (up to 70-80% ). Therefore, time-lapse V S imaging enabled by DAS can be a powerful tool for seismic monitoring of the near surface.