Glacial Isostatic Adjustment, Intraplate Strain, and Relative Sea Level Changes in the Eastern United States

Abstract

AbstractDetermining the motion of the North American plate is difficult due to horizontal intraplate deformation, caused mainly by glacial isostatic adjustment (GIA) in the parts of the plate that are not deforming tectonically. Determination of plate motions also depends on whether the geocenter of the geodetic reference frame coincides with the center of plate rotation. Any difference/error in the International Terrestrial Reference Frame geocenter will introduce an apparent deformation of the plate. We address the plate rotation and what correction models can best account for this internal deformation. We use continuous GPS sites located far from active tectonic boundaries to derive the velocity field in the eastern United States with uncertainties based on a colored noise model. We hypothesize that the velocities will be described by a rigid plate model once the deformation due to GIA and any geocenter/plate rotation center errors have been removed. We find the smallest intraplate residuals with both a geocenter correction and the ICE‐6G model applied. We further compare the coastal GPS vertical velocities with mean relative sea level change rate and find a ~1.9 mm/year difference, which matches the long‐term average global sea level change rate from tide gauges. The entire North American plate is deforming when analyzed at the ~1 mm/year level, and there is no instantaneously stable part due to the long‐wavelength GIA deformation. An accurate estimate of plate rotation cannot be determined from a geographic subset of the plate but only by removing the strain component via a GIA model or a simultaneous estimation of the spatially varying strain rate.