Widespread Occurrence of a High-Velocity Basal Layer in the Pacific Crust Found with Repetitive Sources and Sonobuoys

  1. John G. Heacock
  1. G. H. Sutton,
  2. G. L. Maynard and
  3. D. M. Hussong

Published Online: 15 MAR 2013

DOI: 10.1029/GM014p0193

The Structure and Physical Properties of the Earth's Crust

The Structure and Physical Properties of the Earth's Crust

How to Cite

Sutton, G. H., Maynard, G. L. and Hussong, D. M. (1971) Widespread Occurrence of a High-Velocity Basal Layer in the Pacific Crust Found with Repetitive Sources and Sonobuoys, in The Structure and Physical Properties of the Earth's Crust (ed J. G. Heacock), American Geophysical Union, Washington D. C.. doi: 10.1029/GM014p0193

Author Information

  1. Hawaii Institute of Geophysics, University of Hawaii, Honolulu, Hawaii 96822

Publication History

  1. Published Online: 15 MAR 2013
  2. Published Print: 1 JAN 1971

ISBN Information

Print ISBN: 9780875900148

Online ISBN: 9781118664049

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Keywords:

  • Asper method;
  • Fiji and Manihiki plateau;
  • Hawaiian Islands;
  • High-velocity basal layer;
  • Moho velocity;
  • Murray fracture zone;
  • Oceanic crust;
  • Seismic velocity sections

Summary

Recent innovations in seismic field techniques make it possible to identify a high-velocity basal crustal layer (about 7.1 to 7.7 km/sec, averaging 7.4 km/sec) at several locations in the Pacific Ocean basin. This layer, which usually is masked and is primarily identified from second arrivals: has been only infrequently reported from seismic Ineasurements. Use of a repetitive airgun source, however, shows that it occurs widely in the Pacific Ocean: in the Central basin southwest of the Ha,vaiian Islands; off the California coast; near the Murray fracture zone at about 155°W; and on the Fiji plateau. Twenty-one crustal columns analyzed to date have sufficient penetration to define deep crustal parameters. All these columns exhibit normal deep oceanic velocity structure above the high-velocity basal layer. Furthermore, all the stations except those off California and in the Fiji area have normal oceanic abyssal depths. The thickness of the high-velocity basal layer averages about 3.1 km and results in an increase in the total thickness of the crust compared to that obtained from interpretations that do not include this layer. In the past, a high-velocity basal layer had occasionally been reported from widely scattered locations in the oceans, generally on or adjacent to geologic structural features, and the layer was identified variously as either anomalous crust, upper mantle, or the result of misleading data. However, similar high-velocity layering under continents is well substantiated. Indications are that the layer may well exist under most or all ocean basins. The widespread occurrence of such a layer would have major significance, for both interpretation of other geophysical data (gravity and surface waves) and speculations on the geologic processes that resulted in the formation of the earth's crust.