with broad regional surveys covering several hundred kilometers, 

 followed by increasingly detailed surveys of features a few 

 kilometers to a few meters wide, using deep towed sensors, seafloor 

 photography, and bottom stations. Later, research submersibles will 

 be used. 



In later 1971 and early 1972 an aeromagnetic survey and initial 

 ship surveys by research vessel Knorr, U.S.N.S. Hayes and ships of 

 the Naval Oceanographic Office (NAVOCEANO) were made. The 

 bathymetry from these surveys was combined to develop a 100- 

 fathom contour map of the FAMOUS area. 



In the fall of 1972, comprehensive sampling, mapping, and bottom 

 photography were undertaken by the Jean Charcot near 37 degrees 

 N., and similar techniques were employed by Atlantis 11 using 

 bottom transponder navigation. 



In the spring of 1973, NAVOCEANO completed a very detailed 

 bathymetric survey over the central rift valley from about 36 degrees 

 to 37 degrees N., from which a set of detailed bathymetric charts, 

 some with a 5-fathom contour interval, have been prepared. 



In the summer of 1973, several ships, including the Knorr, operated 

 in the area, using the Scripps Deep Tow package. The Shackleton 

 used ocean bottom seismographs, the D'entrecasteau did detailed 

 bathymetric surveying with 200- to 300-meter line spacing, the 

 Discovery used the 20-ton Gloria side-scan system to make a side- 

 scan mosaic of the area, and the Atlantis II studied 

 microearthquakes with sonobuoys and bottom heat flow. 



In the fall of 1973, the Hayes was used to deploy other bottom 

 seismographs. Later Mizar undertook large-scale bottom 

 photography with the new LIBEC camera system and, on a 

 subsequent cruise, recalled the bottom seismographs and planted 

 ocean bottom current meters, which in turn were recalled by Lynch 

 late in 1973. 



The geophysical surface studies have provided the broad and 

 intermediate scale plate tectonics framework essential for 

 interpretation of the fine-scale, direct seafloor observations to be 

 made with manned research submersibles and near bottom sensors. 

 The primary scientific objective of the initial geophysical surveys 

 was to isolate those regions of the ridge crest where a simple pattern 

 of seafloor spreading could be recognized and where the crest is 

 offset by a transform fault or fracture zone. 



The subsequent surface ship investigations have provided insight 

 to the location and extent of geomorphologic expression of the zone 

 of crustal formation or intrusion in the rift valley and enabled 

 development of a preliminary geologic map of the prospective dive 

 areas. The near bottom geological data allows analysis of the origin 

 of topography by locating fault systems and mapping local volcanic 



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