Reconstruction of groundwater-induced gravity effects using a physical hydrological model at Lhasa Station, Tibetan Plateau

Study region

Lhasa Superconducting Gravimeter (SG) Observatory, Lhasa River alluvial plain

Study focus

The Lhasa SG Observatory is the only continuously operating SG station on the Tibetan Plateau. Surrounded by thick Quaternary sediments, this site provides a critical window into the interactions between tectonic processes and hydrological mass redistribution. Precisely isolating gravity interference caused by local groundwater storage changes is essential for detecting subtle geodynamic signals, such as crustal thickening. We integrated high-precision SG observations, meteorological forcing, and in-situ groundwater levels (2010–2020) into a 1D physically-based Richards equation framework. We reconstructed the spatiotemporal evolution of soil moisture within the 3-meter unsaturated zone to accurately quantify the gravity effects induced by localized hydrological dynamics.

New hydrological insights for the region

The physical model’s reconstruction exhibits strong consistency with SG residuals at an hourly scale (cross-correlation coefficient: 0.62), significantly outperforming global hydrological products like ERA5 (0.18) and GLDAS (0.55). Groundwater-induced gravity fluctuations reach an amplitude of 10.62 μGal (1 μGal = 1⋅10⁻⁸ m s^− 2), sufficient to mask contemporaneous tectonic signatures. Crucially, long-term regression identifies a persistent gravity decline of approximately –0.27 ± 0.002 μGal·a^⁻¹ driven by continuous groundwater depletion. This trend accounts for nearly 14 %–40 % of the observed absolute gravity variation rate. Neglecting station-scale hydrological corrections can thus lead to substantial misjudgments of crustal thickening rates and Moho subsidence magnitudes on the Tibetan Plateau.