Gravimetric Determination of Densities of Seamounts Along the Bonin ARC

  1. Barbara H. Keating,
  2. Patricia Fryer,
  3. Rodey Batiza and
  4. George W. Boehlert
  1. Takemi Ishihara

Published Online: 18 MAR 2013

DOI: 10.1029/GM043p0097

Seamounts, Islands, and Atolls

Seamounts, Islands, and Atolls

How to Cite

Ishihara, T. (1987) Gravimetric Determination of Densities of Seamounts Along the Bonin ARC, in Seamounts, Islands, and Atolls (eds B. H. Keating, P. Fryer, R. Batiza and G. W. Boehlert), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM043p0097

Author Information

  1. Geological Survey of Japan, 1-1-3 Higashi, Yatabe, Ibaraki, 305 Japan

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1987

ISBN Information

Print ISBN: 9780875900681

Online ISBN: 9781118664209

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Keywords:

  • Seamounts;
  • Coral reefs and islands

Summary

A new term “effective depth” is defined as the water depth including the nonlinear effect on a complete Bouguer correction. A least-squares method is used to determine the densities of seamounts from the linear relationship between free-air anomaly and the effective depth, which is calculated by applying a two-dimensional FFT to the bathymetric data. Densities of 19 seamounts along the Bonin Arc are determined using this least-squares method. For seven seamounts including two calderas and two islands, the densities are recalculated removing gravity effects of simple inner structures, which are inferred from the apparent density variations as functions of search radii. Generally speaking, with a track spacing less than 3 nautical miles and with a range of effective depths greater than 1 km, the densities can be determined with an accuracy of 0.05 g/cc. The determined densities have a wide range from 2.4 to nearly 3.0 g/cc. A relationship is recognized between densities of seamounts and their mean depths: the density increases with the depth and a prominent change in the rate of increase is seen at a depth of about 1 km. This is probably due to a decrease in porosity with increase in the depth. A clear pattern of densities is recognized for seamounts with mean depths of about 2 km: a density lower than 2.67 g/cc corresponds to an andesitic volcano and a density higher than 2.67 g/cc corresponds to a basaltic volcano. Two calderas are associated with high Bouguer anomalies.