a) Observed phase velocity map for Rayleigh waves at 167 s (Laske and Masters, 1996). The phase velocity perturbation typically varies between -1.5% and 1.5%. b) After the correction for crustal signal, these variations are substantially larger. c) Observed phase velocity map for Rayleigh waves at 40 s (Ekstrom et al., 1993). d) Map corrected for crustal signal. The crust correction at this period does not increase the variance but redistributes the anomalies.