Seismic reflection study of the geologic structure underlying southern Narragansett Bay, Rhode Island

Abstract

A subbottom reflection survey of southern Narragansett Bay, Rhode Island was made by means of a continuous seismic reflection technique (the Continuous Seismic Profiler)developed at the Woods Hole Oceanographic Institution (Knott and Hersey, 1956). The observational program was conducted in May, 1958 under contract with the Corps of Engineers, U. S. Army, and in May, 1960 under contract with the Bureau of Ships, U . S. Navy, to obtain foundation data for locating hurricane barriers (Corps of Engineers, 1957) and to develop techniques for studying the geologic structure of shallow water areas. At the Woods Hole Oceanographic Institution this work is part of a continuing, broader program directed toward describing the structures and tracing the geologic history of continental margins. The Continuous Seismic Profiler employs a wide-band sound source the pulses from which are reflected from the bottom and from sediment and rock layers beneath the bottom. The sound pulse is synchronized with the sweep of a Precision Graphic Recorder (PGR), which records sound energy received at an underwater detector. (In 1958 the sound source was an early form of the Sparker, while in 1960 the Edgerton Thumper was the source. (These instruments are described below.) When the sound source and the detector are towed from a boat, the reflected sound energy is recorded to present a continuously correlated picture of subbottom structure. Measurements in Narragansett Bay were made south of the Jamestown Bridge in the West Passage and between Conanicut Island and Newport Neck in the East Passage (Fig . 1A and lB). Two additional traverses were made across the bay in areas to the north where core data are available (Fig. 2).