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APPENDIX A EARTHQUAKE-PREDICTION RESEARCH IN THE UNITED STATES M. Nafi Toksoz In the United States, efforts in earthquake prediction have evolved in two directions: l. Studies of seismicity and recurrence times, statistical predic- tion, and risk evaluation based on statistical information. 2. Deterministic prediction based on changes in measurable physical parameters during the interval prior to the earthquake. There have also been experiments during the past decade in the direct control of earthquakes through injection of fluid into the fault zone. In U.S. attempts at earthquake prediction, the earliest emphasis was on statistical methods. At present, however, the deterministic tech- niques hold great potential. This appendix briefly reviews the work and results in the U.S. in earthquake prediction and in experiments toward earthquake control. SEISMICITY AND STATISTICAL PREDICTION It is generally accepted that seismicity patterns of the past hold the key to those of the present and the future. An area that has experi- enced earthquakes in the past will most likely have similar ones in the future, and the frequency and magnitudes of these future earthquakes can be generally estimated from the frequency-magnitude relationships of those of the past. Thus, early attempts to predict earthquakes were based on the seismic history of the area being studied. Using such historic and statistical data, an earthquake risk map (Figure l) was prepared for the United States(l). This map has been used extensively in construction codes and in planning. The major shortcoming of the statistical approach has been that it provides neither exact locations nor reliable recurrence intervals for the larger earthquakes(2). Statistical techniques have been used in many studies to search for periodicities or other trends conducive to more definitive prediction of earthquakes. Most of these studies suf- fered from the unavailability of data covering sufficiently long time periods. The historic data, based on observer reports rather than 37