Monitoring groundwater variations with ambient noise correlations in Beijing

SUMMARY We conduct a seismological monitoring study for groundwater fluctuations within the 12-yr period of 2012–2023 in Beijing using relative seismic velocity changes (dv/v) from continuous ambient noise data. Our measured dv/v time-series agree with groundwater level changes observed from groundwater wells and reveal significant characteristics on hydrological and other environmental changes. The most intriguing feature is a dv/v increase of ∼0.02 per cent in winter, which is interpreted as the imprint of frozen ground perhaps associated with decoupling between air pressure and groundwater. In addition, a rapid reduction of dv/v during the second half of 2021 indicates the development of a groundwater recharging event resulting from heavy rainfall. The long-term trends of dv/v suggest a groundwater rebound from 2018 to 2023 over the study area, which we attribute to increased precipitation, recharging due to the South-to-North Water Transfer Project and reduced irrigation.