Current day Vertical Land Motion in Metropolitan Hot-spots of Southeast United States

Abstract:

Relative sea-level rise (RSLR), the combination of rising sea and subsidence or uplift of the land, is mainly driven by the Vertical Land Motion (VLM) along the southeast coast of the United States. Various processes acting at different spatial temporal scales contribute to VLM. Along the southeast United States, Glacio-Isostatic Adjustment manifests as a long term and broad uplift rate (~2 mm/yr), while anthropogenic processes related to seasonal groundwater and oil withdrawal lead to localized subsidence signals at much smaller spatial and temporal scales. The latter, often not well captured by the existing sparsely distributed (50-100 km) GNSS network.

In this study, we take advantage of high-resolution Sentinel-1 InSAR observations to complement the GNSS network and focus on highly populated areas. We use publicly available standard InSAR products, provided by the JPL Advanced Rapid Imaging and Analysis (ARIA) project, supplemented with manually processed products, to generate VLM maps at 90m spatial sampling over key metropolitan areas in Virginia, North Carolina, South Carolina and Georgia; covering the cities of Norfolk, Hampton, Virginia Beach, Wilmington, Myrtle Beach, Charleston and Savannah. We applied advanced time-series InSAR processing (ARIA-tools and MintPy) in combination with tropospheric noise corrections, estimated from weather model outputs, to estimate vertical VLM trends over the Sentinel-1 record (2014-2020). We used long-term GNSS solutions provided by the Nevada Geodetic Laboratory to correct InSAR for residual long-wavelength errors and propagate uncertainties accordingly. Our results exhibit spatial variation of subsidence within the populated areas of the southeast coast that were not captured from GNSS alone. We found hot spots in Savannah, GA (Skidaway island) and Myrtle Beach, SC which exhibit VLM rates reaching up to 5-6 mm/yr. Norfolk, VA, Wilmington, NC and Charleston, SC show VLM rates of 1-3 mm/yr. Localized signals in areas of anthropogenic activity (such as dredging) exceed these values in small scales.