Zero-frequency upscaling in TTI media

In order to define the affective medium from a stack of layers with TTI ansiotropy, the Schoenberg-Muir theory is used. Resulting medium possesses the monoclinic symmetry that can be approximated as a TTI in one plane. The effective anisotropy parameters and the tilt angle are defined as function of intrinsic tilt angles. It is shown that effective tilt is always smaller than intrinsic ones. The reduction in tilt is controlled by the contrast in elastic properties between the layers.