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4. Bullen, K.E. (1960). A new method of deriving seismic velocity distributions from travel time data. Geophys. J., R. Astr. Soc., 3 258–269.
5. Dahm, C.G. (1936). Velocities of P and S waves calculated from the observed travel times of the Long Beach earthquake. Bull. Seismol. Soc. Amer., 26, 159–171.