Key points are not available for this paper at this time.
The method proposed by Mendiguren (1977) to determine the source parameters from free oscillation data is applied to the July 31, 1970 deep Colombian earthquake. The results indicate a source propagation horizontally for about 150 km along the lithosphere and cutting across its width. The slab behaves as a guide for source propagation. The horizontal propagation velocity is determined as 3.8 km/sec. The intensity of the source grew proportionally to the second power of the propagation distance. This rate of source intensity growth may be interpreted either by a fan-shaped fault model or by a cone shaped volume source. The average slip and stress drop are estimated as 360 cm and 300 bars for the fault model. For the volume source model the transformational shear strain and stress,are estimated as ll X l0 -5 and 160 bars. There is no evidence of a double couple radiation preceeding the P origin time. It is shown that the isotropic and deviatoric cornponents of the moment tensor cannot be uniquely resolved when only observations of a single mode are available. It is observed that, from an statistical basis, the,available oSn data for the Colombian shock can be equally well explained by a pure deviatoric source mddel or by a source model including an isotropic component. Numerical experiments indicate that the inclusion of higher mode data does not change this situation. But, on the other hand, numerical experiments, show that the available data and the scheme used for the inversion would not result in a solution including an artificial implosive component if the actual source were pure deviatoric, If the departure from a pure deviatoric source is produced by noise, it has to be non random, as it could be produced by lateral heterogeneities not included in the inversion scheme.
A. et al. (Fri,) studied this question.