Sensitivity analysis of crustal correction for calculation of lithospheric mantle density from gravity data

We investigate how uncertainties in seismic and density structure of the crust propagate to uncertainties in mantle density structure. The analysis is based on interpretation of residual upper-mantle gravity anomalies which are calculated by subtracting (stripping) the gravitational effect of the crust from the observed satellite gravity field data (GOCE Direct release 3). Thus calculated residual mantle gravity anomalies are caused mainly by a heterogeneous density distribution in the upper mantle. Given a relatively small range of expected compositional density variations in the lithospheric mantle, knowledge on uncertainties associated with incomplete information on crustal structure is of utmost importance for progress in gravity modelling. Uncertainties in the residual upper-mantle gravity anomalies result chiefly from uncertainties in (i) seismic V P velocity-density conversion for the crust and (ii) uncertainties in the seismic crustal structure (thickness and average V P velocities of individual crustal layers, including the sedimentary cover). We examine the propagation of these uncertainties into determinations of lithospheric mantle density and analyse both sources of possible uncertainties by applying different velocity-to-density conversions and by introducing variations into the crustal structurewhich correspond to typical resolution of high-quality and low-quality seismic models. We apply our analysis to Siberia (the West Siberian Basin and the Siberian Craton) for which a new regional seismic crustal model, SibCrust, has recently become available. For the same region, we also compute upper-mantle gravity and density anomalies based on three global crustal models (CRUST 5.1, CRUST 2.0 and CRUST 1.0) and compare the results based on four different crustal models. A large uncertainty in the V P -to-density conversion may result in the uncertainty in lithospheric mantle density anomalies of ca. 0.02-0.03 g cm -3 (i.e. 0.5-1 per cent, which is comparable to compositional density anomalies expected for ...