A global isostatic gravity model of the Earth
The long-wavelength features of the external gravity field of the Earth contain the gravitational signal from deep-seated lateral mass and density inhomogeneities sustained by dynamic Earth mantle processes. To interpret the observed gravity field with respect to mantle dynamics and structures, it i...
| Published in: | Geophysical Journal International |
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| Main Authors: | , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1999
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| Subjects: | |
| Online Access: | http://gji.oxfordjournals.org/cgi/content/short/136/3/519 https://doi.org/10.1046/j.1365-246x.1999.00731.x |
| Summary: | The long-wavelength features of the external gravity field of the Earth contain the gravitational signal from deep-seated lateral mass and density inhomogeneities sustained by dynamic Earth mantle processes. To interpret the observed gravity field with respect to mantle dynamics and structures, it is essential first to remove the lithosphere-induced anomalous gravitational potential, which is generated by the topographic surface load and its isostatically compensating masses. Based upon the most recent global compilation of crustal thickness and density data and the age distribution of cooling oceanic lithosphere, residual topography and gravity are calculated by subtracting the ‘known’ crustal and oceanic lithosphere compensating masses and gravitational effects from the surface fields. Empirical admittances between residual topography and gravity are then computed to estimate the effective depths of the remaining compensating masses, which are not explained by the initial data and model assumptions. This additional compensation is eventually placed by adjusting the density in the uppermost mantle between the Moho and, on average, 70 km depth, with a maximum of 118 km under Tibet. The lithospheric mass distribution is used in a subsequent forward computation to create a global model of the lithosphere-induced gravitational potential. The resulting isostatic model is considered to be valid for spatial wavelengths longer than 500 km. The isostatic lithosphere model field, expressed in terms of both gravity and geoid heights, is subtracted from the observed free-air gravity field to yield a global set of 1°×1° isostatic gravity disturbances and from a satellite-derived long-wavelength geoid to yield the isostatic residual geoid. The comparison of residual (mantle) gravity, residual topography and isostatic corrected gravity allows us to identify the main characteristics of the underlying mantle; for example, dynamic support by mantle flow of the North Atlantic topographic high. Applying the isostatic correction, ... |
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