ISSN:0149-0419    

DOI:10.1080/15210608009379367

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Much new information exists on the long‐term geologic motions of the ocean floor. Horizontal motions, when averaged over a few million years, are approximately 10 to 100 km/m.y. Relative motions across transform faults are twice these values. Uplift of the ocean crust in the rift mountains may be at a rate of 40 km/m.y. for short periods of time. Broader thermal cooling drops the ridge at a rate of about .175 km/m.y. for 1 m.y. old crust, and at a rate of about .02 km/m.y. for 80 m.y. old crust. Near subduction zones the ocean crust subsides at a rate of 2–4 km/m.y. near the oceanic trench axis and 40–60 km/m.y. on a Wadati‐Benioff zone which dips at 45°. Seamounts subside at a rate of .02‐.06 km/m.y. which is comparable to the rate of subsidence due to cooling of the oceanic crustal plates, but two or three orders of magnitude slower than seafloor spreading rates or the subsidence in some Wadati‐Benioff zones.

ISSN:0149-0419    

DOI:10.1080/15210608009379368

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Although acoustic transponder navigational techniques have been given growing application in deep sea research over the last ten years, their precision, as normally used, has not improved during that period. It now appears, however, that with careful attention to transponder design, environmental circumstances, and computational methods the present one‐meter uncertainties can be brought down to the centimeter range, making true geodetic application in the seafloor spreading context a feasible prospect. Newly designed echo repeater type transponders with accurately known time delays can provide 10μsec or less uncertainty in travel time measurement. Environmental data (primarily near bottom temperature profiles) show that even near spreading centers where hydrothermal activity is expected a properly designed transponder based system, including an instrument to makein situsound speed measurements to a part in 105, can give the sound velocity information necessary to achieve centimeter precision over the necessary kilometer path lengths.

ISSN:0149-0419    

DOI:10.1080/15210608009379369

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Tectonic and volcanic activity along the East Pacific Rise near Lat. 21°N is generally restricted to a 3–4‐km‐wide area centered over the rise axis. The East Pacific Rise is a medium‐rate (60 mm/yr) spreading center characterized by modest (100–200 m) relief of hills and seapeaks across the crestal region that is typical for such spreading centers. Few tectonic features appear in an axial volcanic zone 600–1, 200 m wide characterized by fresh, glassy pillow basalt and little or no sediment cover. This volcanic terrain is commonly flanked by tectonic zones where older lavas are cut by numerous normal faults bounding horst and graben systems and open fissures; these tectonic zones are commonly of unequal width on each side of the central volcanic zone and locally may be absent on one side. Bottom photographs and visual observations from a manned submersible indicate that most faults and fissures in the tectonic zones are young. Farther than 2 or 3 km from the axial volcanic zone, recent tectonic activity appears limited to a few faults that bound linear abyssal hills with total offset, suggesting relatively minor extension, so that instrumentation to measure the rate of plate separation along the rise crest will have to span both the volcanic and tectonic zones. The total width of the active plate boundary is at least 20 km, although less than 10% of the separation of the oceanic plates is accounted for by fault displacement and open fissures observed in the tectonic zones and on adjacent rise flanks. The asymmetric widths of the extensional tectonic zones result from migration of the volcanic extrusive zone over time.

ISSN:0149-0419    

DOI:10.1080/15210608009379370

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Photography by Infrared: Its Principles and Applications(third edition ofPhotography by Infraredby Walter Clark), by H. Lou Gibson (John Wiley & Sons, 1978), xxiv + 545 pp., hardcover, $29.95.

ISSN:0149-0419    

DOI:10.1080/15210608009379371

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/15210608009379372

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/15210608009379366

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor