The role of viscoelastic flows excited by earthquakes in driving short-term polar motions is investigated analytically by means of a four-layer model consisting of an elastic lithosphere, a thin asthenosphere, a mean mantle, and an inviscid core. We have employed a linear Maxwell rheology throughout the entire mantle to describe large-scale geodynamic processes for time spans less than 100 years. The global displacement fields which contribute to the perturbations of the moment of inertia are calculated by solving a two-point boundary value problem in which the forcing function is a dislocation source. The elements of the perturbed inertia tensor are then employed directly in the Liouville equations for determining the changes of the Chandler wobble and the rate of the earth's rotation as a consequence of large earthquakes. A complete set of solutions to the Liouville equation is used for this problem. This formulation requires the usage of two classes of eigenspectra: one arising from isostatic reequilibration of the mantle due to faulting and the second set involving the gradual readjustment of the spin axis as a result of transient flows in the mantle. We find that the polar motions depend sensitively on the viscosity structure of the asthenosphere and not at all on the underlying mantle. On the basis of the observed polar motion data and the secular changes of the gravitational harmonic coefficient J2, we can rule out a global low-viscosity zone with short-term asthenospheric viscosities less than about 5¿1018 Pa s and widths greater than 50 km.