A comparative moment tensor inversion study of the Chilean event of March 3, 1985 is performed usng very long period Rayleigh wave data from the IDA and GEOSCOPE networks. It is shown that the perturbing effects of lateral heterogeneity ont he propagation of the Rayleigh waves, especially in the amplitudes, can be minimized if first arriving trains R1 and R2 only can be used. More stable estimates of the main sources parameters can then be obtained as well as an estimate of source directivity compatible with the aftershock distribution and body wave results.