The effect of a strong earthquake on the Free Core Nutation (FCN) and the Free Inner Core Nutation (FICN) is computed in order to dry to explain the energy (McCarthy and Luzum, 1995; Dehant et al., 1995) found from VLBI observations in the FCN and FICN frequency bands. The mass redistribution caused by an earthquake induces changes in the products of inertia of the Earth. For the angular momentum conservation equation, we substitute the elements of the increment of the inertia tensor by their expressions in function of the earthquake parameters as given by Dahlen (1971, 1973). The simplicity of the earth model then allows one to find analytical expressions for the nutations, wobbles and polar shift in terms of the changes in the products of inertia. With these expressions, changes in obliquity and in longitude are calculated for a few large earthquakes. These numerical results show that seismic activity cannot be the excitation mechanism for the FCN and/or FICN.