Full Title: Multi-beam sonar study of the Mid-Atlantic Ridge rift valley, 36°–37°N
Authors: J.D. Phillips and H.S. Fleming
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Projection: Mercator; Scale 1:36,457; Contour interval: 25 fathoms.
Abstract: The SONARRAY array sonar echo-sounding system (of the U.S. Naval Oceanographic Office) has been used to construct high-resolution, 5-fm (9.2-m) contour interval bathymetric charts and profiles over the median and transform rift valleys of the FAMOUS area (~4,200 km2). Only about three days of ship time were required to obtain the bathymetry data. The high speed and resolution of array-type sonar systems result from the fact that a wide swath perpendicular to the ship's track is continually insonified by many narrow beams rather than by a single beam directly beneath the ship. Beam forming and positioning is accomplished by electronic simulation of attitude information provided by the ship's inertial navigation systems. Analysis of the SONARRAY-derived charts and profiles has revealed several new distinctive topographic features characteristic of the oceanic ridge axis here. Specifically: low-relief (~100-m elevation) linear hills form the median rift valley inner floor ; narrow (~1 km), flat-topped terraces and benches with outward-facing antithetic scarps characterize the median rift walls; quasi-circular (~10-km diam.) nodal basins are found at the intersection of the transform faults with the median rift valley; and narrow (~2 km) trough and ridge lineaments found along the transform rift valley floors probably mark the sites of recent horizontal faulting.
Published: 1/01/1978
Pages: 12, plus 4 sheets
Product Category: Maps and Charts