Seismic Refraction Measurements in the Atlantic Ocean Basin

Abstract

A reversed seismic refraction measurement was made in 2800 fms. of water at Latitude 34°N., Longitude 66°30'W. (120 miles northwest of Bermuda and 400 miles east of Cape Hatteras). The ocean floor was found to be composed of two layers. A velocity of 24,800 ft. per sec. (7.58 km. per sec.) was found for the second layer. This was identified with the Pn waves of earthquake seismology attributed to the basaltic layer found below the Mohorovicic discontinuity. A first layer was clearly present, but the velocity was not determined. A velocity of 5600 ft. per sec. (1.70 km. per sec.) was assumed, giving a thickness of 4500 feet for this sedimentary layer. This velocity was chosen from some of our earlier measurements, as yet mostly unpublished. The granitic and intermediate layers are thus absent beneath the ocean floor at this point. The velocity of the basaltic layer compares favorably with those of Slichter in New England and with Jeffreys' world average. A detailed report of this work is being submitted for publication to the Journal of the Seismological Society entitled, Seismic refraction measurements in the Atlantic Ocean Basin, Part I, by Maurice Ewing, J. L. Worzel, J. B. Hersey, Frank Press, and G. R. Hamilton.