1. Eaton, J. P., and Murata, K. J., Science, 132, 925 (1960).
2. Tsai, Y., and Aki, K., Trans. Amer. Geophys. Un., 50, 238 (1969).
3. Press, F., Phys. Earth and Planet. Int. (in the press).
4. Kanamori, H., Phys. Earth and Planet. Int. (in the press).
5. Ewing, M., and Press, F., Bull. Seismol. Soc. Amer., 44, 471 (1954).