The Geoid: Effect of compensated topography and uncompensated oceanic trenches

Geophysical Research Letters
By:  and 

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Abstract

The geoid is becoming increasingly important in interpretation of global tectonics. Most of the topography of the earth is isostatically compensated, so removal of its effect from the geoid is appropriate before tectonic modeling. The oceanic trenches, however, are dynamically depressed features and cannot be isostatically compensated in the classical way. Continental topography compensated at 35 km gives intracontinental geoidal undulations of up to 15 m over mountain ranges in a spherical harmonic expansion to order and degree 22. Oceanic topography compensated at 40 km, reasonable for the thermally supported long wavelengths, matches the +10 m difference between old continents and old oceans in a detailed NASA/GSFC geoid. Removing the assumed compensation for the oceanic trenches leaves negative anomalies of up to 9 m amplitude caused by their uncompensated mass deficit. This mass deficit acts as a partial "regional compensation" for the excess mass of the subducting slabs, and partly explains why geoidal (and gravity) anomalies over the cold slabs are less than thermal models predict.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The Geoid: Effect of compensated topography and uncompensated oceanic trenches
Series title Geophysical Research Letters
DOI 10.1029/GL009i001p00029
Volume 9
Issue 1
Year Published 1982
Language English
Publisher American Geophysical Union
Description 4 p.
First page 29
Last page 32