1. Alekseev, A. S., Babich, V. M., andGel'chinsky, B. Ya. (1961),Ray Method of Evaluation of the Intensity of Wave Fronts, Voprosy Dyn. Teor. Raspr. Seis. Voln.5, 5?21 (in Russian).
2. Babich, V. M. (1979),The Space-time Ray Method in Elastic Wave Propagation, Izv. Acad. Sci. USSR. Phys. Solid Earth5, 87?93.
3. Babich, V. M., andKiselev, A. P. (1989),Nongeometrical Waves ? Are there Any? An Asymptotic Description of Some' Nongeometrical' Phenomena in Seismic Wave Propagation, Geophys. J. Int.99, 415?420.
4. Buchen, P. W. (1974),Application of the Ray-series Method to Linear Viscoelastic Wave Propagation, Pure and Appl. Geophys.112, 1011?1030.
5. ?ervený, V., Molotkov, I. A., andP?en?ik, I.,Ray Method inSeismology (Charles University Press, Prague 1977).