20 Nov (GEOL) Karen Williams, Geophysics

Speaker: Karen Williams, The Virginia Polytechnic Institute and State University

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

Time: Thu, 20 Nov, 4:30pm

Location: Exploratory 1309 and via Zoom (for link, email lhinnov@gmu.edu)

Host: Linda Hinnov

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 Positioning System (GPS) campaign data throughout the Chesapeake Bay. The new campaign measurements were combined with continuous GPS data from the region covering the same time-period and processed to produce new estimates of vertical velocities and their associated uncertainties. We investigate two proposed long-term, geologic sources of subsidence throughout the Chesapeake Bay: dynamic topography and glacial isostatic adjustment. Dynamic topography is the response of the Earth’s surface due to the convecting mantle. Glacial isostatic adjustment is the response of the Earth’s surface to the growth and decay of global ice sheets. We perform geodynamic modeling to assess the influence of both processes on the region. 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. A comparison with vertical land motions from 50 years ago 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. Further, this 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.