Figure 19 Nazca Plate 



The East Pacific Rise extends northward 

 into the Gulf of California where high heat 

 flow values and swarms of microseisms have 

 been recorded. Scientists from the Scripps 

 Institution of Oceanography and the Univer- 

 sity of Mexico are making a detailed study of 

 the associated rift valley because of its anal- 

 ogy to the Red Sea rift valley, where heavy 

 metals have been detected in the hot brines. 



Mid-Atlantic Ridge 



Better understanding of the geological pro- 

 cesses operating along mid-ocean ridges is the 

 basis for a study of the Mid-Atlantic Ridge. 

 Despite numerous individual studies of this 

 feature, knowledge is really quite limited, and 

 nothing is known at scales smaller than ap- 

 proximately 20-50 km. 



Prior to undertaking a major study of the 

 Mid-Atlantic Ridge, IDOE supported a Na- 

 tional Academy of Sciences workshop to 

 examine major questions concerning the pro- 

 cesses operating along the crest. Scientists 

 from Canada, France, Iceland, the Nether- 

 lands, the United Kingdom and several U.S. 

 institutions met at Princeton in January 1972. 



The workshop results summarize our present 

 knowledge and outline a comprehensive pro- 

 gram for a concerted attack on the major 

 problems.- 



The workshop identified five programs as 

 high-priority field projects, as follows: 



• Long-range (l,600-to-2,000 km) seismic 

 refraction measurements to provide in- 

 formation on the geometry and physical 

 properties of the deeper lithosphere, the 

 asthenosphere and the transition zone — 

 with emphasis on variations with dis- 

 tance from the accreting plate boundary 

 (i.e., the Mid-Atlantic Ridge]. 



• Detailed geological and geophysical stud- 

 ies, to include interdisciplinary surveys 

 on a rifted ridge crest, a nonrifted ridge 

 crest, a large equatorial transform fault 

 and a fractured plate. 



• Comprehensive geological and geophysi- 

 cal surveys, particularly short-line seis- 

 mic refraction and dredging to obtain a 

 complete set of rock samples from 72°N 

 to 36°N. Also suggested are reconnais- 

 sance surveys in the South Atlantic, just 

 south of the highly fractured equatorial 

 region. 



• Bottom stations and instruments to re- 

 cord seismic signals from natural or man- 

 made sources, water currents, tempera- 

 ture, magnetic and electric variations, 

 chemical concentrations in seawater, 

 pressure and other variables. The report 

 notes that many such instruments, while 

 within the state of the art, nevertheless 

 need to be developed. 



• Island stations and studies, including 

 seismograph stations on islands on or 

 near the ridge crest to define details of 

 seismic activity on ridge crests and in 

 fracture zones, deep drilling (3-to-4 km) 

 into the axial zone, continued geodetic 

 measurements on Iceland and the deploy- 

 ment of hydrophones in the Sofar Chan- 

 nel from a variety of island stations as 

 a means of locating microseisms. 



Scientific exploration of the ocean floor will 

 enter a new phase with the Mid-Atlantic 



2 Understanding the Mid-Atlantic Hidge, A Compre- 

 hensive Program, National Academy of Sciences, 

 Washington, D. C, 1972. 



33 



