Understanding the geodetic signature of large aquifer systems: Example
of the Ozark Plateaus in Central United States
Abstract
The continuous redistribution of water mass involved in the hydrologic
cycle leads to deformation of the solid Earth. On a global scale, this
deformation is well explained by redistribution in surface loading 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 central United States. We begin
by characterizing the most important sources of signal in the spatially
heterogeneous groundwater level dataset using an Independent Component
Analysis. Then, to estimate the associated poroelastic displacements, we
project geodetic time series corrected for surface loading effects onto
orthogonalized versions of the 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 surficial layers with a high fracture
density. Our findings suggest that OPAS undergoes significant
poroelastic deformation, including highly heterogeneous horizontal
poroelastic displacements.