Fiber‐Optic Seismic Full Waveform Monitoring of Groundwater Dynamics

Abstract Understanding groundwater dynamics is critical for sustainable water management, particularly as climate extremes become more intense and frequent. However, the resolution of existing subsurface observational tools remains inadequate for detailed aquifer monitoring and imaging. We introduce an innovative technique for groundwater monitoring using time‐lapse full‐waveform inversion, leveraging fiber‐optic cables as dense sensors and vehicular traffic as repetitive seismic sources. Over a two‐year period along Sandhill Road, California, this approach captures detailed spatiotemporal S‐wave velocity variations, revealing a 2.9% reduction corresponding to a 9.0‐m groundwater table rise following atmospheric river storms in Water Year 2023. Notably, our analysis enables high‐resolution daily estimates of aquifer recharge rates. We also observe spatially inhomogeneous subsurface responses, with less reduction beneath impervious paved zones than grassy areas, showcasing the importance of urbanization on the natural recharge of aquifers. Our method has the potential for high‐resolution spatiotemporal monitoring and quantitative characterization of groundwater systems.