1. A method of simulating a borehole response of an anisotropic formation in the crust of the earth, the method comprising: formulating a geometric model of the formation, the geometric model comprising a plurality of layers definable in a cylindrical coordinate system defined by an axial direction normal to each of the layers, a radial direction relative to the axial direction, and a circumferential direction relative to the axial direction; formulating a computational model of wave propagation in the formation, the computational model comprising one or more field variables and a wave equation describing a behaviour of the one or more field variables, wherein the one or more field variables are represented as respective Fourier series expansions of π-periodic harmonics in the circumferential direction, and numerically solving the computational model.