Iterative ratio method: A method to map the depth to the Moho from gravity anomalies using linear approximate invariance

Interfaces characterized by a density contrast are common models to interpret gravity data. Two key parameters of the interface inversion are the density contrast and constant offset, which are free parameters. We aim to iteratively estimate the two free parameters by a new method: the iterative-ratio (ITRAT) method. This method is based on the linear approximate invariance of the depth and free parameters and the availability of several depth constraints. The free parameters are estimated iteratively to update the interface depth. By processing the synthetic Moho model, we find that the ITRAT method generally converges after two iterations with good accuracy for the free-parameter estimates and Moho depth. Random tests for the constant density model indicate that the accuracy of the ITRAT method is slightly affected by the noise of gravity data and the number of constraints, but it is sensitive to the uncertainty of the constraints. For the variable density model, the ITRAT method will estimate a constant density contrast and constant offset to obtain a Moho model, which has a lower depth error than the model with a mean density contrast. The new method is finally demonstrated by mapping the Moho of the Santos Basin (Brazil) according to the depth constraints and regional gravity anomalies.