FREE OSCILLATIONS OF THE EARTH

In this article, we review the step-by-step progress made in the recent past towards the solution of the problem of the free oscillations of the Earth. The equations of motion for the toroidal and the spheroidal oscillations of a spherically-symmetric, non-rotating, elastic, isotropic (SNREI) Earth model are given. These equations can be expressed in the form dY/dr = A(r)Y, where Y is a (6 x 1) matrix in the case of the spheroidal oscillations and a (2 x 1) matrix in the case of the toroidal oscillations. The effect of the rotation of the Earth on its free oscillations and the method of calculating the dispersion of surface waves on a sphere are briefly mentioned.