Regional gravity inversion of crustal thickness beneath the Tibetan plateau

Abstract

We apply a newly developed inversion scheme for a gravimetric determination of the Moho depths. This scheme utilizes the system of observation equations, which relates the complete crust-stripped gravity disturbances (i.e., the gravity disturbances corrected for anomalous crustal density structures) with the (unknown) Moho depths by means of a linearized Fredholm integral equation of the first kind. A point-value discretization scheme is applied, in which the coefficients of a design matrix are calculated using the closed analytical formula for the integral kernel function. The a priori error model is not applied due to the lack of knowledge on the accuracy of crustal density structure model. Tikhonov’s regularization is applied to stabilize the ill-posed solution; the regularization matrix is the identity matrix and the regularization parameter is selected based on an optimal fitting of the gravimetric solution to the a priori seismic Moho model. This method is applied to determine the Moho depths regionally at the study area of the Tibetan plateau and Himalayas characterized by the world largest crustal thickness. A constant value of the crust-mantle density contrast of 485 kg m−3 is assumed in our numerical model. For this density contrast, the estimated maximum Moho depths in central Tibet exceed 80 km.