Geodetic and Geodynamic Constraints on Vertical Land Motions in the Chesapeake Bay

Abstract

The Chesapeake Bay, a region of high financial, historical, and ecological value, experiences the highest rates of relative sea-level rise on the East Coast of the United States. Regional land subsidence enhances sea-level rise, however quantified rates of vertical land motions vary substantially in published solutions and the precise drivers are not well understood. From 2019 to 2023, a collaborative effort led by the USGS was conducted to collect new Global Navigation Satellite System (GNSS) campaign data (51 stations) throughout the Chesapeake Bay. The new campaign measurements were combined with continuous GNSS data from the region covering the same time-period (120 stations) and processed with GAMIT-GLOBK to produce new estimates of vertical velocities and their associated uncertainties. Further, we use the Robust Network Imaging algorithm to interpolate the vertical land motions solution and find ubiquitous subsidence across the Chesapeake Bay ranging from -2.97 to -0.40 mm/yr. Two proposed long-term, geologic and tectonically-linked sources of subsidence throughout the Chesapeake Bay are dynamic topography and glacial isostatic adjustment. We perform geodynamic modeling to assess the influence of both processes on the region. We estimate present-day rates of dynamic topography using ASPECT (Advanced Solver for Planetary Evolution, Convection, and Tectonics) and vertical land motions due to glacial isostatic adjustment using SELEN (SealEveL EquatioN solver). By isolating the long-term processes contributing to subsidence throughout the Chesapeake Bay, the short-term geological and anthropogenic sources of localized vertical land motions, such as water-use practices, can be better resolved. Our findings indicate a negligible contribution from dynamic topography to present-day rates of vertical land motions on the order of -0.02 to 0.03 mm/yr. Rates of land subsidence driven by glacial isostatic adjustment range from approximately -0.5 to -2.5 mm/yr depending on the underlying assumptions of the model. In this dissertation, chapter one focuses on dynamic topography, chapter two addresses glacial isostatic adjustment, and chapter three presents our final vertical velocity solution. The final vertical velocity solution indicates ubiquitous land subsidence throughout the Chesapeake Bay with varying rates at major cities. A comparison with geodetically-derived vertical land motions from 1974 indicate shifts in the major subsidence regions and changes in subsidence rates. These results have advanced our understanding of the geophysics of the Chesapeake Bay and can be used to help stakeholders in the area make more informed decisions regarding the impacts of regional subsidence. Our work highlights the importance of regular monitoring of vertical land motions, which can improve projections of relative sea-level changes and their associated coastal hazards for communities in the Chesapeake Bay region.