Weak asthenosphere beneath the Eurasian interior inferred from Aral Sea desiccation

Abstract

The rheology of the lower crust and upper mantle influences Earth’s plate tectonic style of mantle convection, yet its spatial variability is poorly resolved, particularly in continental interiors. Here we use satellite radar interferometry to map the delayed uplift resulting from the desiccation of the Aral Sea, which has lost ~1,000 km3 of water since 1960. From this we constrain the rheology of the underlying upper mantle by elastic and viscoelastic modelling. We find a long-wavelength uplift of up to ~7 mm yr–1 between 2016 and 2020 that decays radially from the Aral Sea. This uplift pattern is best explained by viscoelastic relaxation of the asthenosphere below a strong lithospheric mantle. We estimate that the asthenosphere has an effective viscosity of 4–7 × 1019 Pa s below 130–190 km depth, slightly larger than the values inferred from post-seismic deformation at subduction zones, but 1–2 orders of magnitude smaller than estimates from glacial isostatic adjustment in other tectonically stable regions. Such uplift highlights the potential for human activities to influence deep-Earth dynamics and the interconnectedness of surface and mantle processes. The drying out of the Aral Sea has induced flow of the relatively weak asthenosphere beneath, demonstrating that human activity can influence mantle dynamics, according to numerical simulations of ground uplift measured by radar interferometry.