Attenuation of seismic waves of very low frequency

The quality factor of the free oscillations of the earth is calculated from the observed time rate of decay of the energy. Records of the I.P.G.P. long-period data acquisition system are used, after a process enhancing a chosen mode, so that the scatter in the Q results is reduced. Determination of attenuation is made for the spheroidal and torsional fundamental modes and two torsional higher modes.The attenuation of seismic waves is determined from the decay of energy of standing-wave patterns with time, and from the damping of travelling waves with distance, using the surface mantle waves recorded at a single I.P.G.P. long-period seismic station after each great circle path (Gaulon, 1971).