By comparing records of the radial component of motion of teleseismic P waves to records of the vertical component, it is possible to identify S phases within the P wave form. These phases are generated by the mechanism of P to S conversion at discontinuities in velocity under the receiving station. Similar phases of the S to P converted type appear as precursors to the direct SV arrival. Models for the crustal structure can be tested by generating synthetic seismograms for both components of motion of both the P and SV waves and comparing with the data. The technique has been used to model the crustal structure at WWSSN stations CAR and COR. It has also been used to check a recently proposed model for the crustal structure in eastern Canada which contains a large low-shear-velocity zone at the base of the crust. This study indicates that the crustal structure in eastern Canada is highly non-uniform with perhaps few features common to the whole region. Finally, the technique is used to identify several stations in the WWSSN which appear to be located on highly anomalous structure.