The GOCE Estimated Moho Beneath the Tibetan Plateau and Himalaya

Abstract

A better understanding of the physics of the Earth’s interior is one of the key objectives of the ESA Earth Explorer missions. This work is focused on the GOCE mission and presents a numerical experiment for the Moho estimation under the Tibet-Quinghai Plateau and the Himalayan range by exploiting the gravity data collected by this mission. The gravity observations, at satellite level, are first reduced for the topography, oceans and known sediments and then the residual field is inverted to determine the crust–mantle interface. The uniqueness of the solution is guaranteed using this simplified two-layer model by making assumptions on the density contrast. Our inversion algorithm is based on the linearization of the Newton’s gravitational law around an approximate constant Moho depth. The resulting equations are inverted by exploiting the Wiener–Kolmogorov theory in the frequency domain and treating the Moho depth as a random signal with zero mean and its own covariance function. As for the input gravity observations, we considered grids of the anomalous gravitational potential and its second radial derivative at satellite altitude, as computed by applying the so called space-wise approach to 8 months of GOCE data. Errors of these grids are available by means of Monte Carlo simulations. Taking a lateral density variations for granted, the Moho beneath the Tibetan Plateau and Himalaya is computed on a grid covering the whole area with an accuracy of few kilometers and an estimated resolution of about 250 km. Taking into account this resolution, the estimated Moho generally shows a good agreement with existing local seismic profiles. The areas where this agreement is not so good can be clearly attributed to the presence of anomalies in the crust–mantle separation, such as subduction zones. The GOCE-only solution is finally improved by using seismic profiles as additional observations, locally increasing its accuracy and resolution.