Understanding the Geodetic Signature of Large Aquifer Systems: Example of the Ozark Plateaus in Central United States.

The continuous redistribution of water involved in the hydrologic cycle leads to deformation of the solid Earth. On a global scale, this deformation is well explained by the loading imposed by hydrological mass variations and can be quantified to first order with space‐based gravimetric and geodetic measurements. At the regional scale, however, aquifer systems also undergo poroelastic deformation in response to groundwater fluctuations. Disentangling these related but distinct 3D deformation fields from geodetic time series is essential to accurately invert for changes in continental water mass, to understand the mechanical response of aquifers to internal pressure changes as well as to correct time series for these known effects. Here, we demonstrate a methodology to accomplish this task by considering the example of the well‐instrumented Ozark Plateaus Aquifer System (OPAS) in the central United States. We begin by characterizing the most important sources of groundwater level variations in the spatially heterogeneous piezometer dataset using an Independent Component Analysis. Then, to estimate the associated poroelastic displacements, we project geodetic time series corrected for hydrological loading effects onto the dominant groundwater temporal functions. We interpret the extracted displacements in light of analytical solutions and a 2D model relating groundwater level variations to surface displacements. In particular, the relatively low estimates of elastic moduli inferred from the poroelastic displacements and groundwater fluctuations may be indicative of aquifer layers with a high fracture density. Our findings suggest that OPAS undergoes significant poroelastic deformation, including highly heterogeneous horizontal poroelastic displacements. Plain Language Summary: A number of hydrological processes can deform the solid Earth. Measuring this deformation through space‐based geodesy offers an opportunity to study these hydrologic processes and infer properties of the sub‐surface. In the case of an aquifer, surface displacements can arise from changes in total water mass, which load the Earth, as well as from changes in groundwater pressure which alter stresses in the aquifer and in the surrounding medium. In this study, we describe a methodology to extract and separate these distinct but related deformation signals from Global Navigation Satellite System time series and hence infer mechanical properties of the aquifer system by using satellite gravimetry data, local groundwater level measurements as well as a blind source separation technique. We also present a mathematical framework to study surface displacements resulting from variations in groundwater pressure in a medium with heterogeneous elastic properties. We demonstrate the methodology in the Ozark Plateaus Aquifer System in the central United States. Key Points: We characterize seasonal and multiannual fluctuations in groundwater levels with an Independent Component AnalysisWe separate and model the hydrological loading and poroelastic deformation fields captured by global navigation satellite systemWe infer relatively low elastic moduli from the extracted poroelastic displacements and groundwater fluctuations [ABSTRACT FROM AUTHOR]