VERTICAL CRUSTAL MOVEMENTS ALONG THE EAST COAST, NORTH-AMERICA, FROM HISTORIC AND LATE HOLOCENE SEA-LEVEL DATA

Sea-level data from eastern North America are analyzed for evidence of neotectonism, which is inferred from residual sea-level anomalies, after removal of glacial isostatic and eustatic components. The sea level is examined on two different time scales, using long-term Holocene paleosealevel indicators, and short term (≤ 100 yrs) tide-gauge records. The major process affecting Holocene sea levels in this region is the continuing response to glacial unloading. The northward migration of the collapsed bulge peripheral to the retreating ice sheets is clearly delineated by the displacement of the hingeline between glacioisostatic subsidence and uplift from around 43° to 48°N, over the last 14,000 years. Similarly, the zone of maximal subsidence (collapsed forebulge) has moved from ~ 36°-42°N prior to 11,000 years to 44°-46°N during the last 5000 years. Tide-gauge data for the East Coast covering the last 100 years indicate a sea-level rise of around 2-4 mm/yr. Subtraction of the late Holocene trend reduces the regional mean from 2.72 ± 0.71 mm/yr to 1.26 ± 0.78 mm/yr, which is close to the value (1.47 ± 0.68 mm/yr) obtained by using viscoelastic model corrections (after Peltier, 1986). Thus, nearly half of the recent regional sea level rise appears to be of glacioisostatic origin. The corrected mean regional trend lies within a few tenths of a mm/yr of the estimated mean global eustatic trend (~1.1 mm/yr; Gornitz and Lebedeff, 1987). Generally, the results show no evidence for major tectonic movements, especially for large fault offsets. Nevertheless, several anomalous areas persist, that are suggestive of gentle warping, after glacioisostatic and eustatic processes have been taken into account. These correspond to areas with known Neogene epeirogenic movements, and include the region between Savannah, Georgia-Charleston, South Carolina (subsidence), Cape Fear Arch (uplift), southern Chesapeake Bay (Late Pleistocene-Holocene uplift, succeeded by recent subsidence), Montauk and the Long Island platform (uplift?). Subsidence in the Charleston area and southern Chesapeake Bay may be in part caused by groundwater withdrawal. © 1990.