SEISMIC REFRACTION MEASUREMENTS IN THE ATLANTIC OCEAN. PART IV: BERMUDA, BERMUDA RISE, AND NARES BASIN

Abstract

This report describes the results of a series of refraction profiles made in the vicinity of the Bermuda Islands and along two lines of traverse extending south and southeast of Bermuda to the northern perimeter of the Nares Basin. On the profiles made near the Nares Basin four seismic layers were determined—an unconsolidated sediment with average velocity of 1.70 km/sec, consolidated volcanics and/or sediments with average velocity of 4.51 km/sec, a basement with average velocity of 6.63 km/sec, and a second basement with average velocity of 8.03 km/sec. The boundary between the two basements corresponds with the Mohorovicic discontinuity and is at an average depth of 10 km; the material above the Mohorovicic discontinuity corresponds in velocity with the intermediate layer of continental seismology. Over the Bermuda Rise only one high velocity basement was determined. The thickness of the consolidated volcanics and/or sediments decreases from about 4.5 km. to .5 km. away from Bermuda, and the thickness of the unconsolidated sediment decreases from about .8 km. to about .1 km. away from Bermuda. The boundary between these two layers corresponds with the “M” reflection horizon of deep sea reflection measurements. Important structural features are the depressions in the basement and the disappearance of the Mohorovicic discontinuity on the Bermuda Rise. On the profiles made in the vicinity of the Bermuda Islands, the truncated cone of the Bermuda volcanoes is measured with an average velocity of 4.25 km/sec. The results of the depth calculations from these profiles, the deep boring on Hamilton Island, and the known geology of the islands are in agreement with Daly9s (1910) hypothesis on the effects of glaciation on atolls.