Space-Time Monitoring of Groundwater via Seismic Interferometry

Historic levels of droughts are plaguing the globe, raising a vital call for sustainable freshwater management. Urgently needed is a refined understanding about the structures and dynamics of underground aquifers. Here we present a novel approach for in-situ monitoring of groundwater fluctuations by making use of existing seismograph arrays in California. By advancing the seismic interferometry techniques, we manage to measure not only the temporal evolution but also the spatial distribution of Relative Changes in Seismic Velocity (Δv/v) in the Coastal Los Angeles Basins during 2000-2020. We find Δv/v to recover the hydraulic head, illustrating the potential of leveraging seismometers to propel the temporal and spatial density of well measurements. Images of Δv/v seasonality agree with surface deformation inferred from InSAR, but also further enable the characterization of aquifers and their hydrology at different depths. Long-term Δv/v suggest that distinct trends (decline or recovery) of groundwater storage occurred in adjacent basins, due to anthropogenic pumping practices compounding the effect of climate change. This pilot application bridges the gap between seismology and hydrology, and shows the promise of using seismometers to monitor, image and evaluate underground hydrologic processes. We anticipate Δv/v to be a unique type of 4D geodata that will bring new insights to studying various time-varying processes in Earth’s shallow subsurface.