1. A method of determining a rock facies in a subterranean region of the Earth at a first location, comprising the steps of: obtaining seismic data associated with said region; selecting a plurality of facies; providing a first rock physics probability distribution with spatial dependencies; providing a second rock physics probability distribution around the first location comprising at least one probability distribution per facies, wherein the spatial dependencies in the first rock physics probability distribution are utilized, such that the second rock physics distribution provides a simplifying approximation of the first rock physics distribution; performing a Bayesian inversion at the first location by a computer processor using the second rock physics probability distribution to predict the probability of the rock facies at said location taking into account said seismic data, in order to indicate a presence of said facies in said region; and correcting for deviations of the approximating distribution at the first location with a correction term to reproduce the rock physics probability distribution at the first location.