1. A method for upscaling geomechanical properties, comprising: mapping fine cells from a geological model to a coarse cell from a geomechanical model; assigning mechanical properties to each of the fine cells based, at least in part, on the geological model, wherein the mechanical properties comprise elastic and plastic parameters of the geomaterials represented by the fine cell; simulating material response characteristics of the coarse cell to various boundary conditions based on the mechanical properties assigned to each of the fine cells; and computing upscaled mechanical properties of the coarse cell based on the material response characteristics of the coarse cell.