Abstract
Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Earth’s lithosphere and viscous asthenosphere. A more satisfactory test of isostasy is to determine the depth to and density contrast between crust and mantle at the Moho discontinuity (Moho). Generally, the Moho can be mapped by seismic information, but the limited coverage of such data over large portions of the world (in particular at seas) and economic considerations make a combined gravimetric-seismic method a more realistic approach. The determination of a high-resolution of the Moho constituents for marine areas requires the combination of gravimetric and seismic data to diminish substantially the seismic data gaps. In this study, we estimate the Moho constituents globally for ocean regions to a resolution of 1° × 1° by applying the Vening Meinesz-Moritz method from gravimetric data and combine it with estimates derived from seismic data in a new model named COMHV19. The data files of GMG14 satellite altimetry-derived marine gravity field, the Earth2014 Earth topographic/bathymetric model, CRUST1.0 and CRUST19 crustal seismic models are used in a least-squares procedure. The numerical computations show that the Moho depths range from 7.3 km (in Kolbeinsey Ridge) to 52.6 km (in the Gulf of Bothnia) with a global average of 16.4 km and standard deviation of the order of 7.5 km. Estimated Moho density contrasts vary between 20 kg m-3 (north of Iceland) to 570 kg m-3 (in Baltic Sea), with a global average of 313.7 kg m-3 and standard deviation of the order of 77.4 kg m-3. When comparing the computed Moho depths with current knowledge of crustal structure, they are generally found to be in good agreement with other crustal models. However, in certain regions, such as oceanic spreading ridges and hot spots, we generally obtain thinner crust than proposed by other models, which is likely the result of improvements in the new model. We also see evidence for thickening of oceanic crust with increasing age. Hence, the new combined Moho model is able to image rather reliable information in most of the oceanic areas, in particular in ocean ridges, which are important features in ocean basins.
Highlights
The Mohorovičić discontinuity is the interface, which marks the boundary between both the oceanic crust and continental crust from underlying mantle
As a final product we have derived a global model of the marine Moho depth (MD) and Moho density contrast (MDC) with aresolution of 1 1
The model, named COMHV19, employs the GMG14 satellite altimetry-gravimetry model corrected with the Earth2014 Earth topographic/bathymetric model and other non-isostic effects on gravity in a Vening Meinesz-Moritz type solution combined in a weighted least square procedure
Summary
The Mohorovičić discontinuity (or Moho) is the interface, which marks the boundary between both the oceanic crust and continental crust from underlying mantle. In case of the gravimetric method, gravity data are employed under a certain isostatic hypothesis, implying that the Moho model is characterized by some simplified hypothesis to guarantee the uniqueness of the solution of the inverse gravitational problem (Reguzzoni et al, 2013), while in the seismic studies, Moho models are mostly determined from refracted and reflected waves, and sometimes by receiver functions and the ambient noise technique (Kind et al, 2012; Shapiro and Campillo, 2004). The global crust models based on seismic methods are locally very accurate, they are typically sparse, over areas without adequate seismic data, where they could yield unrealistic results with large uncertainties. Over large parts of the world with a limited coverage of seismic data, in particular in marine areas, the combination of seismic and gravimetric data (i.e combined approach) is essential
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