CLIMATIC AND TECTONIC DRIVERS OF SHORT-TERM AND LONG-TERM VERTICAL LAND MOVEMENT IN NEW YORK

UNAVCO, a government funded research institution, provides access to hundreds of continuously operating GPS station records throughout the United States. GPS signals display both long-term and seasonal trends. We examine GPS signals in the northeastern US from 2006-2019. Long period vertical movement in this region is chiefly a result of glacial-isostatic adjustment (GIA) resulting from deglaciation at the end of the Pleistocene Epoch. The vertical movements display slow uplift or subsidence consistent with GIA (Herring et al., 2016), with the hinge aligned east-west through central New York, and uplift north of the hinge and subsidence south of it. GIA and plate motion are not the only signals present in the GPS records. The GPS vertical movement exhibits high frequency fluctuations, with seasonal cycles. Fluctuations, ignoring outliers, can range from 25 to 50 mm on periods that range from days to a year or more. On average, the signal lows fall during January and February, and reach peaks during September and October. We hypothesize that the main driver of velocity fluctuations are crustal responses to hydrologic cycling. We compare GPS and nearby river records to identify climate signatures that leak into GPS records. We find no correlation at daily intervals between discharge and vertical motion, and a weak correlation at annually averaged values. At seasonal scales, we find a much stronger anti-correlation between discharge and vertical motion. Hydrologic loading of the crust suppresses vertical motion. GPS records averaged by month display a decrease in the rate of subsidence south of the hinge line at Binghamton, Long Island, and Cortland during early spring to late summer, when river flows reach a minimum. A reverse trend occurs in winter months when subsidence increases. The same held true northeast of the hinge line in stations such as Oneonta where vertical motion increased during summer but decreased during the winter months. Hydrologic fluxes account for up to a 10 mm difference in average monthly movement in our study area.