1. A method of generating a wellsite design, comprising: designing a workflow for a mechanical Earth Model; building, using a computer processor, an initial mechanical Earth Model based on said workflow adapted for modeling drilling and completions operations in a hydrocarbon reservoir, wherein said initial mechanical Earth Model includes workflow models comprising a framework model, a petrophysics model, a mechanical stratigraphy model, a rock strength model, an overburden model, a pore pressure model, a stress direction model, and a horizontal stress model; calibrating each of said workflow models thereby generating a calibrated mechanical Earth Model by: (a) observing wellsite conditions thereby generating observations for each of said workflow models; (b) performing simulations to thereby generate predictions for each of said workflow models, wherein said predictions comprise elastic properties of intact rock and a characterization of open natural fractures from said mechanical stratigraphy model; (c) comparing said observations with said predictions; (d) accepting said initial mechanical Earth Model, thereby generating a calibrated mechanical Earth Model, on the condition that said observations agree with said predictions; (e) adjusting each of said workflow models on the condition that said observations do not agree with said predictions; and (f) repeating steps (b) through (e) until said observations agree with said predictions; identifying boundaries in said calibrated mechanical Earth Model based on said elastic properties and said characterization of said open natural fractures; and generating said wellsite design based on said boundaries in said calibrated mechanical Earth Model.