Isostatic global gravity fields for geodetic and geophysical applications
20/09/2016 | 09:45 | Session 2: Model Development
Author(s): Pavel Novak, Robert Tenzer, Mohammad Bagherbandi, Wenjin Chen and Lars Sjöberg
Pavel Novak, Robert Tenzer, Mohammad Bagherbandi, Wenjin Chen and Lars Sjöberg
Different theoretical models were proposed to explain the isostatic compensation mechanism. The Airy-Heiskanen and Pratt-Hayford isostatic hypotheses are particularly well known. They assume that the topographic mass surplus and the oceanic mass deficiency are locally isostatically balanced by either a varying depth or density of compensation. The Vening-Meinesz Moritz isostatic (flexural) model represents a more realistic assumption of the regional compensation mechanism described for the Earth’s homogenous crust. A more refined version of this isostatic model takes into consideration also the crustal density heterogeneities. These compensation schemes are applied here to compile global maps of the isostatic gravity disturbances. The isostatic gravity fields are then used to analyze their spatial and spectral characteristics with respect to the global crustal geometry. Results reveal that each of the applied compensation model yields a distinctive spatial pattern of the resulting isostatic gravity field with its own spectral characteristics. The Airy-Heiskanen isostatic gravity disturbances provide a smooth gravity field with no correlation with the crustal geometry, while revealing the gravitational signature of deep mantle density heterogeneities. The Pratt-Hayford isostatic gravity disturbances are highly spatially correlated with the topography on land while provide a smooth gravity field over oceans. These two isostatic gravity fields are thus suitable in physical geodesy applications for gravity data interpolation or prediction, particularly using the Airy-Heiskanen isostatic gravity disturbances on land and the Pratt-Hayford isostatic gravity disturbances over oceans. Since the Vening-Meinesz Moritz isostatic model represents more closely the actual isostatic mass balance, these isostatic gravity data are preferably used for a Moho recovery. We also demonstrate that the complete crust-stripped isostatic gravity disturbances reveal a gravitational signature of the mantle lithosphere. These isostatic gravity data are thus suitable in studies of the lithospheric mantle structure, while information on the deep mantle density structure is comprised in the long-wavelength spectrum of the Airy-Heiskanen isostatic gravity field.