Oral Presentation

Water mass transfers near the Earth’s surface, whether due to natural hydrologic processes or human activity, can deform the lithosphere and interact with fault systems. Characterizing how the solid Earth responds to these forcings provides crucial insights into both hydrological processes and the rheology and crustal dynamics of our planet. Over the past two decades, satellite geodetic techniques such as Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) have enabled the measurement of Earth’s surface deformation with increasingly high spatial coverage, resolution, and accuracy. Yet, extracting hydrological deformation signals from geodetic datasets that contain multiple sources of deformation and noise remains challenging.

Here, we use the well-instrumented Sacramento Valley as a case study to demonstrate a new methodology for characterizing hydrology-driven geodetic deformation. Combining satellite-based observations of land surface deformation (GNSS and InSAR) and mass fluctuations (GRACE/-FO) with thousands of in situ groundwater level and geological log measurements reveals three distinct deformation regimes: (1) elastic deformation due to large-scale hydrological loading, (2) poroelastic aquifer deformation due to groundwater extraction and natural recharge, and (3) abrupt inelastic compaction during the 2020-2022 drought. The resulting high-resolution map of poroelastic deformation provides constraints on the spatially heterogeneous elastic properties of the Sacramento Valley and reveals a sharp transition in deformation amplitudes along the Dunningan Hills fault line. Our findings have important implications for groundwater and land subsidence management in California and highlight the complex interactions between groundwater dynamics, crustal deformation, and fault processes.