Georges Jobert; Travel-time equations and energy propagation for an elastic, heterogeneous, isotropic medium: Correction and approximate inversion. Bulletin of the Seismological Society of America ; 63 (6-1): 1967–1971. doi:
Expressions identical to the formulas of a preceding paper are obtained when due allowance is made for the variation of quantities which were erroneously taken as constant. A method for the approximate inversion of the travel-time curves is presented for the case where the surfaces of equal velocity are planes with an infinitesimal dip.