Identification of mantle and lithospheric components of the gravity field by isostatic gravity anomalies |
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Authors: | M E Artemjev T M Babaeva V O Mikhailo I E Voydetsky |
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Institution: | (1) Institute of Physics of the Earth USSR Academy of Sciences, Moscow, USSR |
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Abstract: | All anomalous masses of the Earth are reflected in the free air gravity anomalies and the geoidal undulations. The low viscosity
of the asthenosphere significantly reduces the possibility of existence of density inhomogeneities in the layer. This fact
provides some physical basis for the separation of the gravity field anomalies. It has been shown by power spectrum analysis
of the free air anomalies and gravity field of isostatically compensated model of the lithosphere for the North Atlantic and
adjacent areas of America, Europe and Mediterranean, that the attraction of isostatically compensated model is significant
for any wave length of the field. It causes significant error in the interpretation if long wavelength constituents of the
free air gravity anomalies are considered as a field of deep anomalous masses. The isostatic anomalies und isostatic geoid
are free from the influences of isostatically compensated lithosphere. The characteristic feature of the isostatic anomalies
power spectrum is a pronounced minimum at the wavelength of about 1000 km. The relative homogeneity of the asthenosphere may
explain this minimum. It means that principal density inhomogeneities of the Earth's interior are separated by the asthenospheric
layer. Such a minimum has not been observed at the power spectrum of free air anomalies being masked by corresponding wavelength
of the field of isostatically compensated lithosphere. Isostatic anomalies that reflect the differences between the real structure
of the lithosphere and its isostatically compensated model have wavelengths less than 1000 km. Isostatic anomalies with the
wavelength more than 1000 km reflect the attraction of density inhomogeneities situated under the level of isostatic compensation.
The basic features of power spectrum of isostatic anomalies are the same for oceanic and continental areas. The method based
on Kolmogorov-Wiener filtration which consideres statistical characteristics of the field has been developed to divide the
isostatic gravity anomalies into lithosphere and mantle components. For the North Atlantic and adjacent areas the field of
mantle inhomogeneities has been determined. |
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