Quantifying seasonal deformation signals using InSAR in Baton Rouge, South Louisiana (2016-2022)

Seasonal land motion can be caused by processes above the surface or underground. These processes often are linked to natural changes in the hydrological cycle. Seasonal deformation can be elastic due to surface loading or poroelastic caused by changes in subsurface fluid storage. We investigate the processes driving the > 15 mm seasonal deformation in the Baton Rouge, Louisiana region which is intersected by the Mississippi and the Amite Rivers. The aquifer system is formed by vertical sands that are almost independent of each other, and it is crossed by the E-W striking Baton Rouge normal fault, which is a leaky barrier. We quantify seasonal motions using Sentinel-1 InSAR time series acquired between 2016-2022. InSAR precision was validated using local GNSS data. We compare the deformation with modeled motions from non-tidal loads (hydrological, oceanic, and atmospheric), river water levels, and modeled groundwater levels. We find that none of the non-tidal loads contributed significantly to the seasonal deformation. The amplitude of the seasonal response has spatial variations related to the distance to the Mississippi River and the Baton Rouge fault. We also identify which layers of the aquifer system are in phase with the observations and are thus most likely to cause poroelastic deformation. The temporal lags between deformation and changes in groundwater levels depend on which aquifer sand is driving the motion. We conclude that seasonal ground deformation in the area is dominantly driven by the poroelastic response to Mississippi River level changes that recharge the shallower aquifer layers.