Comparison of crustal thickness from two gravimetric-isostatic models and CRUST2.0

Abstract

The Mohorovičić discontinuity is the boundary between the Earth's crust and mantle. Several isostatic hypotheses exist for estimating the crustal thickness and density variation of the Earth's crust from gravity anomalies. The goal of this article is to compare the Airy-Heiskanen and Vening Meinesz-Moritz (VMM) gravimetric models for determining Moho depth, with the seismic Moho (CRUST2.0 or SM) model. Numerical comparisons are performed globally as well as for some geophysically interesting areas, such as Fennoscandia, Persia, Tibet, Canada and Chile. These areas are most complicated areas in view of rough topography (Tibet, Persia and Peru and Chile), post-glacial rebound (Fennoscandia and Canada) and tectonic activities (Persia). The mean Moho depth provided by CRUST2.0 is 22.9  0.1 km. Using a constant Moho density contrast of 0.6 g/cm 3 , the corresponding mean values for Airy-Heiskanen and VVM isostatic models become 25.0  0.04 km and 21.6  0.08 km, respectively. By assuming density contrasts of 0.5 g/cm 2 and 0.35 g/cm 3 for continental and oceanic regions, respectively, the VMM model yields the mean Moho depth 22.6  0.1 km. For this model the global rms difference to CRUST2.0 is 7.2 km, while the corresponding difference between Airy-Heiskanen model and CRUST2.0 is 11 km. Also for regional studies, Moho depths were estimated by selecting different density contrasts. Therefore, one conclusion from the study is that the global compensation by the VMM method significantly improves the agreement with the CRUST2.0 vs. the local compensation model of Airy-Heiskanen. Also, the last model cannot be correct in regions with ocean depth larger than 9 km (e.g., outside Chile), as it may yield negative Moho depths. This problem does not occur with the VMM model. A second conclusion is that a realistic variation of density contrast between continental and oceanic areas yields a better fit of the VMM model to CRUST2.0. The study suggests that the VMM model can primarily be used to densify the CRUST2.0 Moho model in many regions based on separate data by taking advantage of dense gravity data. Finally we have found also that the gravimetric terrain correction affects the determination of the Moho depth by less than 2 km in mean values for test regions, approximately. Hence, for most practical applications of the VMM model the simple Bouguer gravity anomaly is sufficient. M. Bagherbandi and L.E. Sjöberg 642 Stud. Geophys. Geod., 55 (2011) K e y wo r d s : crustal thickness, CRUST2.0 model, inverse isostatic problem, isostatic compensation, Moho depth

Reformulation of the Vening-Meinesz Moritz Inverse Problem of Isostasy for Isostatic Gravity Disturbances

“…Sjöberg and Bagherbandi [10] computed the Moho depths based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy (VMM isostatic model). Bagherbandi and Sjö-berg [11] demonstrated that the VMM Moho depths better agree with the Moho data taken from the global crustal seismic model CRUST2.0 (Bassin et al [12]) than those obtained based on solving the Airy-Heiskanen isostatic model.…”

Comparative analysis of Vening-Meinesz Moritz isostatic models using the constant and variable crust-mantle density contrast – a case study of Zealandia

“…Sjöberg and Bagherbandi (2012) demonstrated the advantage of using the combined least-squares method compared to the Airy-Heiskanen model. Bagherbandi and Sjöberg (2011) computed the Moho depths based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy (VMM isostatic model). They demonstrated that the VMM Moho depths generally better agree with CRUST2.0 data than those obtained from using the Airy-Heiskanen isostatic model.…”