Tripartite phase velocity observations in laterally heterogeneous regions

The hypothesis that one can assign the phase velocity calculated, from a tripartite net to one of the legs of the net exclusively, when that leg approximately coincides with the surface wave propagation vector, has been substantiated by experimental data. If more than one leg of an array of stations is parallel to the propagation vector, it is possible to make a quantitative estimate of the lateral heterogeneity of structure across the net. If, however, the propagation vector coincides with only one of the legs, one can only draw qualitative conclusions about lateral heterogeneity.