Optimum choice of parameters and numerical schemes for a regional gravimetric Moho recovery

Abstract

Despite practical limitations of isostatic theories to model the Moho geometry are well-known, gravimetric methods are often used in terrestrial studies of crustal structure in regions with a low seismic data coverage. Moreover, these methods are indispensable in planetary studies. Various gravimetric methods have been proposed. The Airy and Pratt theories are defined based on adopting a local compensation mechanism. The Vening Meinesz theory assumes a regional isostatic flexural model. The Vening Meinesz regional isostatic model generally describes a respond of the lithosphere to a load more realistically than the Airy model over continents. The Pratt method, on the other hand, better describes a compensation mechanism of the oceanic lithosphere. The application of a particular isostatic model also depends on applied numerical procedures, parameters for inversion, input data specifications, and many other aspects. In this study, we address some basic aspects by applying local and regional isostatic models for a Moho recovery. We also conduct a spectral analysis to assess a spectral resolution of gravity data that is optimal for a Moho recovery. Furthermore, we inspect the influence of low-degree spherical harmonics of gravity field on a Moho geometry. Gravimetric results are validated using seismic data at the European plate. Our results confirm a better performance of a regional compensation principle. We also demonstrate that a different thickness of the oceanic and continental crustal thickness should be taken into account as a priori information. Spectral analysis indicates that gravity data used for a Moho inversion should optimally have a spatial resolution between degrees 60 to 180. Results also show that low-degree spherical harmonics do not modify significantly the Moho geometry, particularly over regions with a relatively homogenous structure of deep mantle.