Correlating Groundwater Level Fluctuations of a Fractured Confined Aquifer With Relative Variations in Seismic Velocity: A Way to Estimate the Groundwater Storage

Analysis of ambient seismic noise is of increasing interest for its potential to monitor aquifers, seismic wave velocity being sensitive to fluctuations of the water table or to pore pressure variations. The correlation with groundwater pressure variations in confined aquifers, which are often strategic, is an open scientific question, as is the stored groundwater volume. Based on an experimental site equipped with a low-cost seismometer located close to a borehole in a confined fractured aquifer, we demonstrate that (a) the auto and inter-components correlation of the time series of the seismometer enables detecting variations in seismic velocities, (b) these changes are negatively correlated with the groundwater pressure variations, and (c) these changes occur above a groundwater pressure threshold related to the fractures' properties. Finally, we propose a method to estimate the storage coefficient's order of magnitude of the confined aquifer using the correlation between dv/v and the groundwater pressure.