From measurements of the apparent periods of free oscillations in the spectra of long period records a procedure defines the extraction of systematic residuals with respect to the values for a global model. These shifts are different for different great circle paths and can be attributed to lateral variations of phase velocity. On two examples a comparison is made. showing a quantitative agreement of the result of the procedure with measurements on progressive mantle waves. Thus, residuals obtained from free oscillation data can be used for regionalization as well as those from progressive wave data.