Gravity Anomalies and the Crust of the Earth in the Pacific Basin

  1. Gordon A. Macdonald and
  2. Hisashi Kuno
  1. George P. Woollard and
  2. William E. Strange

Published Online: 21 MAR 2013

DOI: 10.1029/GM006p0060

The Crust of the Pacific Basin

The Crust of the Pacific Basin

How to Cite

Woollard, G. P. and Strange, W. E. (1962) Gravity Anomalies and the Crust of the Earth in the Pacific Basin, in The Crust of the Pacific Basin (eds G. A. Macdonald and H. Kuno), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM006p0060

Author Information

  1. Geophysical and Polar Research Center, University of Wisconsin, Madison, Wisconsin

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1962

Book Series:

  1. Geophysical Monograph Series

Book Series Editors:

  1. Waldo E. Smith

ISBN Information

Print ISBN: 9780875900063

Online ISBN: 9781118669310

SEARCH

Keywords:

  • Bouguer gravity anomalies;
  • Crustal mass distribution;
  • Folded mountain systems;
  • Gravity anomalies;
  • Submarine geology

Summary

Free-air and Bouguer gravity anomalies are related to seismic measurements of crustal thickness throughout the world. A similar study is made of the relation between depth of water in the oceans and crustal thickness established seismically. It is shown that the regional free-air anomaly values, whether in the ocean or on land, are indicative of abnormalities in crustal composition and thickness. Negative anomaly values are shown to be associated with a crust of subnormal density and thickness, and positive anomaly values with a crust of greater than normal density and thickness. The thickness abnormality indicated is the reverse of what would be deduced on the assumption of homogeneous crustal and mantle material. That there is no uniformity in crustal composition or thickness associated with a given surface elevation is demonstrated by comparing gravity data and crustal thickness values for the deep portions of the Atlantic and Pacific Basins. Over the depth range from 5000 to 6000 in, the free-air anomaly values in the Atlantic Basin average about 20 mgal less than in the Pacific Basin. The thickness of crust is found to be also about 2 km less in the Atlantic Basin and the elevation of the M discontinuity about 2 km nearer the surface. Within the Pacific Basin there are similar regional variations in crustal parameters associated with similar regional changes in free-air anomaly values.

An analysis of crustal structure in the East Indies area, based on the empirical relations between the depth of the M discontinuity and Bouguer anomalies, shows that the marked negative isostatic belts are not related so much to a crustal down-buckle beneath the trench as crustal crumpling and thickening inshore from the trench in the transition zone from a thick continental crust to a thin oceanic crust. On the section studied, the negative isostatic anomaly is centered over a well defined topographic rise of some 3000 m where the crust has a thickness of about 20 km. The trench, which occurs on the seaward flank of this crustal bulge, has a near normal oceanic crustal thickness of about 9.0km.