FIG. 9. Strain change associated with the 1993 Okushiri Island, Hokkaido, earthquake recorded at a distance of ≈100 km.

would be impractical for most modern industrialized cities. Then the question is, given this uncertainty, what strategy should be taken for seismic hazard reduction besides the traditional long-term hazard assessment.

A strategy for effective seismic hazard reduction is to take full advantage of the recent technical advancements in seismological methodology and instrumentation, computer, and telemetry technology. In highly industrialized communities, rapid earthquake information is critically important for emergency services agencies, utilities, communications, financial companies and media to make quick reports, and damage estimates and to determine where emergency response is most needed (34). The recent earthquakes in Northridge, California, and Kobe, Japan, clearly demonstrated the need for such information. Several systems equipped to deal with these needs have already been implemented (35, 36). With the improvement of seismic sensors and a communication system, it would be possible to increase significantly the speed and reliability of such a system so that it will eventually have the capability of estimating the spatial distribution of strong ground motion within seconds after an earthquake. Some facilities could receive this information before ground shaking begins. This would allow for clean emergency shutdown or other protection of systems susceptible to damage, such as power stations, computer systems, and telecommunication networks.

FIG. 10. Ratio of the seismic moment of precursory deformation to that of the mainshock (solid and open symbols). Solid symbol indicates upper bound. Horizontal axis is the magnitude.

This research was partially supported by U.S. Geological Survey Grant 1434–95-G-2554. This is Contribution 5555, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125.

1. Turcotte, D.L. (1992) Fractals and Chaos in Geology and Geophysics (Cambridge Univ. Press, Cambridge, U.K.).

2. Working Group on California Earthquake Probabilities (1995) Bull. Seismol. Soc. Am. 85, 379–439.

3. Allen, C.R. (1976) Bull Seismol. Soc. Am. 66, 2069–2074.

4. Mogi, K. (1984) Pure Appl. Geophys. 122, 765–780.

5. Mogi, K. (1985) Earthquake Prediction (Academic, Tokyo).

6. Sato, H. (1970) J.Geol. Soc. Jpn. 15, 177–180 (in Japanese).

7. Sato, H. (1977) J.Phys. Earth 25, Suppl., S115–S121.

8. Kanamori, H. & Cipar, J.J. (1974) Phys. Earth Planet. Int. 9, 128–136.

9. Kanamori, H. & Anderson, D.L. (1975) J.Geophys. Res. 80, 1075–1078.

10. Cifuentes, I.L. & Silver, P.G. (1989) J. Geophys. Res. 94, 643–663.

11. Ihmle, P.F., Harabaglia, P. & Jordan, T.H. (1993) Science 261, 177–183.

12. Kedar, S., Watada, S. & Tanimoto, T. (1994) J. Geophys. Res. 99, 17893–17907.

13. Wyatt, F.K. (1988) J. Geophys. Res. 93, 7923–7942.

14. Linde, A.T. & Johnston, M.J.S. (1989) J. Geophys. Res. 94, 9633–9643.

15. Agnew, D.C. & Wyatt, F.K. (1989) Bull. Seismol. Soc. Am. 79, 480–492.

16. Johnston, M.J.S., Linde, A.T. & Gladwin, M.T. (1990) Geophys. Res. Lett. 17, 1777–1780.

17. Johnston, M.J.S., Linde, A.T. & Agnew, D.C. (1994) Bull. Seismol. Soc. Am. 84, 799–805.

18. Kedar, S. & Kanamori, H. (1996) Bull Seismol. Soc. Am. 86, 255–258.

19. Faculty of Science, Hokkaido University (1993) Report of the Coordinating Committee for Earthquake Prediction (Hokkaido Univ., Hokkaido, Japan), Vol. 52, pp. 45–56.

20. Johnston, M.J.S., Linde, A.T., Gladwin, M.T. & Borcherdt, R.D. (1987) Tectonophysics 144, 189–206.

21. Lorenzetti, E. & Tullis, T.E. (1989) J. Geophys. Res. 94, 12343– 12361.

22. Shibazaki, B. & Matsu’ura, M. (1995) Geophys. Res. Lett. 22, 1305–1308.

23. Kanamori, H. (1972) Phys. Earth Planet. Int. 6, 346–359.

24. Sacks, I.S., Linde, A.T., Snoke, J.A. & Suyehiri, S. (1981) in Maurice Ewing Series 4: Earthquake Prediction, eds. Simpson, D.W. & Richards, P.G. (Am. Geophys. Union, Washington, DC), pp. 617–628.