Dynamic topography, defined as the deflection of the Earth’s surface due to the convecting mantle, causes changes in vertical land motions (VLM). We aim to estimate the effect of dynamic topography on VLM along the North American Atlantic Coast, which is a region where land subsidence influences relative sea-level rise and other coastal hazards. The contribution of dynamic topography to VLM continues to be debated since previous studies show a range in the rate change of dynamic topography for this region, which are in part due to uncertainties in Earth’s rheology. In this investigation, we model global mantle convection to better assess the role of dynamic topography on VLM along the North American Atlantic Coast. We are implementing a time-dependent approach using the finite element code ASPECT (v2.2.0). We constrain our initial temperature conditions using the tomography models SAVANI, GYPSUM, S40RTS, and TX2008 and then explore both linear and non-linear rheological models. The two rheological models allow us to assess differences in the rate change of dynamic topography globally with a nonlinear rheology compared to a linear rheology. We expect this work will allow us to better understand the contribution of dynamic topography to VLM along the North American Atlantic Coast.

Relative sea-level rise is a major coastal hazard affecting about half the population of the United States. The Chesapeake Bay is characterized by the fastest rate of sea-level rise along the Atlantic coast of North America, in part because of land subsidence. Previous studies have quantified a range of land subsidence rates in the Chesapeake Bay (~1-4 mm/yr) from various measurement techniques that contribute to high rates of relative sea-level rise. In this study, we present progress towards developing a new vertical land motion map for the Chesapeake Bay region to provide more robust constraints on estimates of relative sea-level rise. We are using a combination of GNSS observations and InSAR interferograms. Available continuous GNSS data in the region that span November 2014 - September 2020 are processed with GAMIT-GLOBK to align temporally with available Sentinel-1 InSAR satellite data. We are using an approach that combines the two geodetic observations to provide a new solution of vertical land motions for the Chesapeake Bay. Additionally, this project is collecting new campaign GNSS observations across the Chesapeake Bay each fall for 5 years, beginning in 2019. We will also present about the 2020 and planned 2021 campaign GNSS observations, which will ultimately be incorporated into our new map of vertical land motions for the region. The impacts of this work will be improved flooding and inundation hazard maps, as well as updated projections for municipal flood mitigation planning that will be created using the new dataset.