Abstract
AbstractGroundwater is a critical resource for human activities worldwide, and a vital component of many natural ecosystems. However, the state and dynamics of water‐bearing aquifers remain uncertain, mostly due to the paucity of subsurface data at high spatial and temporal resolution. Here, we show that analysis of infrastructure‐generated ambient seismic noise acquired on distributed acoustic sensing (DAS) arrays has potential as a tool to track variations in seismic velocities (dv/v) caused by groundwater level fluctuations. We analyze 5 months of ambient noise acquired along an unused, 23 km‐long telecommunication fiber‐optic cable in the Sacramento Valley, CA, a so‐called “dark fiber." Three array subsections, ∼6 km apart, are processed and the stretching technique is applied to retrieve daily dv/v beneath each location. Near the Sacramento river, dv/v variations in the order of 2%–3% correlate with precipitation events and fluctuations in river stage of ∼1.5 m. In contrast, regions away (2.5 km) from the river do not experience large dv/v variations. These observations reveal short‐scale spatial variability in aquifer dynamics captured by this approach. Dispersion analysis and surface wave inversion of noise gathers reveal that seismic velocity perturbations occur at depths of 10–30 m. Rock physics modeling confirms that observed dv/v are linked to pore pressure changes at these depths, caused by groundwater table fluctuations. Our results suggest that DAS combined with ambient noise interferometry provides a means of tracking aquifer dynamics at high spatial and temporal resolutions at local to regional scales, relevant for effective groundwater resource management.
Highlights
Groundwater constitutes approximately half of all drinking water world-wide, about 40% of the water needed for irrigation in agricultural activities, and one-third of all water used in industrial applications (International Groundwater Resources Assesment Centre, 2018)
Our results suggest that distributed acoustic sensing (DAS) combined with ambient noise interferometry provides a means of tracking aquifer dynamics at high spatial and temporal resolutions at local to regional scales, relevant for effective groundwater resource management
Our results suggest that ambient seismic noise interferometry applied to noise records acquired on DAS arrays, potentially deployed on dark fiber networks, is a promising tool for monitoring groundwater table variations at spatiotemporal scales relevant to achieve sustainable management of groundwater resources
Summary
Groundwater constitutes approximately half of all drinking water world-wide, about 40% of the water needed for irrigation in agricultural activities, and one-third of all water used in industrial applications (International Groundwater Resources Assesment Centre, 2018). A few other studies have demonstrated the potential to use infrastructure-generated noise (frequencies in the order of 5–30 Hz) for local monitoring of natural and artificial changes in groundwater levels with spatial resolution in the order of several tens of meters and temporal sampling of days (Fores et al, 2018; Voisin et al, 2016, 2017) Other techniques, such as seismic interferometry using ballistic waves as opposed to coda waves (Garambois et al, 2019), and single-station methods (Kim & Lekic, 2019) have recently emerged. Our results suggest that ambient seismic noise interferometry applied to noise records acquired on DAS arrays, potentially deployed on dark fiber networks, is a promising tool for monitoring groundwater table variations at spatiotemporal scales relevant to achieve sustainable management of groundwater resources
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