Tehri Reservoir Operation Modulates Seasonal Elastic Crustal Deformation in the Himalaya

The filling and emptying cycles of reservoir operations may change hydrological mass loading, leading to a flexural deformation of the crust that may compromise the infrastructure safety or trigger earthquakes. In this study, we investigate the seasonal crustal response of the Tehri reservoir in the Garhwal Himalaya, northern India, using interferometric synthetic aperture radar (InSAR), Global Positioning System, the Gravity Recovery and Climate Experiment, radar altimetry, and in‐situ water‐level measurements. Results show that the evolution of vertical ground deformation is modulated elastically by the reservoir operation, whereas the horizontal displacement measured near the reservoir exhibits a time lag of ∼65 days with respect to the vertical displacements and water‐level variations. The delayed deformation transients indicate that the reservoir loading/unloading cycles affect the near‐surface hydrology in its neighborhood. The broader distribution and higher amplitude of ground deformation during the loading periods revealed by the InSAR time series can be explained by water–rock interactions, which cause a decrease in the effective Young's modulus within the top 300‐m crustal layer. Our results demonstrate the potential of using space geodetic data to ensure a better understanding of the solid Earth response to regional hydrological changes. Plain Language Summary The seasonal variations of water storage in the reservoir alter the stress state and hydrologic loadings in the neighboring region thereby may bring measurable crust deformation at the lakeshore. Recent studies have worked to capture the long‐term deformation signals near the reservoirs and lakes, but seldom of them has considered the localized crust behavior on a seasonal scale. To better understand crust deformation processes from this anthropogenic source, we used multiple space geodetic observations, in‐situ data, elastic and poroelastic models to study the Tehri reservoir, India. The results show that the ∼80 m water loading cycles modulate the elastic deformation close to the reservoir. An asymmetric crustal deformation with higher amplitude and broader impacted area in the loading scenario, providing a possible weakening effect in the fractured shallow crustal medium from the water‐rock interaction. While the elastic deformation in the vertical direction is well explained, more complicated horizontal motions may be connected to the local hydrologic conditions. Key Points We investi