A computer program was used to evolve a model of compressional and shearwave velocity for the earth's mantle which would be consistent with the travel times given in the Jeffreys-Bullen (J-B) tables. The sensitivity shown by our computed travel times to changes in layer velocities suggests that models containing low-velocity channels would produce travel times different from those given in the tables. Travel times associated with velocity models proposed by others were also computed. The significance of travel-time residuals depends primarily on the reliability of observed travel times for those epicentral distances at which the model fails.

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