what is meant by this term in relation to gravity anomalies: The Andes is isostatically compensated?

Answer 1

Please note that the first two paragraphs of the first answer noted above is taken, verbatim and without attribution, from Hernandez, O.P, and von Frese, R.P.B, 2006, J. Res. Earth Sci, Vol 10, No. 2

The notion of isostatic compensation is that whenever material is added to or taken away from the surface of the Earth, say by mountain building or erosion or transportation, then there is some compensation at subsurface layers so that the Earth tends not to have huge variations in gravity from place to place as a result of density and matter variations. There are some variations, but isostatic compensation keeps them from getting very large.

Answer 2

The Earth's Crust is subject to gravitational stress. Therefore for Gravitationall energy to reacjh equilibrium relatived to one area which is disturbed or depressed another area must conmpensate to form an equilbrium around the circumfernce of the Earth's Crust. So mountain formation that compensate to form equilbrium is called isostatical compensation. It should follow the rules of control system theory.

Answer 3

Recently revised models on global tectonics describe the convergence of the North Andes, Nazca, Caribbean and South American Plates and their seismicity, volcanism, active faulting and extreme topography. The current plate boundaries of the area are mainly interpreted from volcanic and seismic datasets with variable confidence levels. New insights on the isostatic state and plate boundaries of the northwestern Andes Mountains can be obtained from the spectral analysis of recently available gravity and topography data.

Isostatically disturbed terrain produces free-air anomalies that are highly correlated with the gravity effects of the terrain. The terrain gravity effects (TGE) and free air gravity anomalies (FAGA) of the Andes mountains spectral correlation data confirms that these mountains are isostatically disturbed. Strong negative terrain-correlated FAGA along western South America and the Greater and Lesser Antilles are consistent with anomalously deepened mantle displaced by subducting oceanic plates. Inversion of the compensated terrain gravity effects (CTGE) reveals plate subduction systems with alternating shallower and steeper subduction angles. The gravity modeling highlights crustal deformation from plate collision and subduction and other constraints on the tectonism of the plate boundary zones for the region.
Considering that isostatic equilibrium is the ideal state that any uncompensated mass tends to reach through time, implies that any uncompensated mass of the North Andes Mountains is under pressure to adjust vertically and horizontally to reach equilibrium. Therefore, a direct correlation is expected between disturbed and seismically active terrains, whereas minimal seismic activity is expected for isostatically compensated terrains