Neotectonic Activity of Atlantic Inner Continental Margin: ABSTRACT

Abstract

A consistent pattern of neotectonic activity along the inner edge of the Atlantic continental margin is emerging from new data on earthquake activity, contemporary vertical movement and geologic structure. Seismic activity, as shown by both historic and instrumental data, is concentrated in embayments on the Atlantic coastal margin. These are the Southeast Georgia, Salisbury, and Raritan Bay embayments and all major bays and mouths of major rivers in New England. Present-day subsidence is indicated to be taking place at most of these embayments from studies of releveling and tidal-gauge data, Pleistocene and Holocene shorelines, position of historic construction relative to sea level, and archaeological studies. Releveling studies indicate Passamaquoddy Bay, Maine-New Brunswick, is subsiding at a rate of 9 mm per year relative to Bangor, Maine. The embayments appear to have developed as irregularities on the general downwarp of the continental margin by early Tertiary. Many of the embayments occur over older grabens, which may help control their position. The offshore Blake Spur fracture zone trends toward and is aligned with the earthquake activity at Charleston, South Carolina. This fracture zone may also help to control the spacing of the embayments. End_Page 1658------------------------------ The neotectonic activity along the inner continental margin and seismic activity along extensional faults inland from it strongly suggest that slight rifting is still occurring from the opening of the Atlantic. The present downwarping at the continental edge is now concentrated in irregularities, embayments, that possibly developed by sagging over basement structures. End_of_Article - Last_Page 1659------------