Surface waves on a radially stratified earth

It is well known that the normal modes of free oscillations of the earth may be interpreted in terms of surface waves. We elaborate on this connection by demonstrating that a normal mode may be viewed as being physically created by the resonant reinforcement of multiply-circumnavigating surface waves. The dispersion curves for the phase and group velocities of these surface waves may accordingly be determined from the eigenfrequency spectrum of the earth´s oscillations, which is done here using the set of eigenfrequencies empirically obtained by Gilbert and Dziewonski. These “empirical” dispersion curves are compared with global surface wave data furnished by a standard earth model, as well as with local surface wave measurements, and some possibly significant differences are found.