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INTRODUCTION Great excitement currently exists among seismologists over major achieve- ments in our efforts to predict earthquakes. Various physical phenomena precursory to earthquakes have been reported by careful observers for many centuries. In the past, seismologists tended to discount most of these reports, but measurable physical precursors are now coming under intense scientific scrutiny, and many appear to be valid and significant. Indeed, several scientific predictions have already been successful, al- though those that we have been able to fully evaluate are all for small earthquakes. Few seismologists now doubt that physical precursors to earthquakes do in fact exist. But are they sufficiently consistent and uniform to permit development of a routine and reliable prediction sys- tem? And will techniques useful for predicting small earthquakes also work for large earthquakes—the only ones of real social importance? If our capability to predict earthquakes does become a major scien- tific reality, it will be the second large advance in the earth sciences in the last decade. The first has been the concept of plate tectonics, which developed explosively over about the past l5 years and was gener- ally accepted by the late l960's. In many ways, this concept was a major stimulus to the work on prediction. Small earthquakes have been successfully predicted by reputable in- vestigators in the United States, Japan, and the Soviet Union, and several large, damaging earthquakes may already have been successfully predicted in the People's Republic of China. In each of these areas, many failures and false alarms have also occurred. There is not at present a sufficient scientific basis for issuing, with a high degree of confidence, an authoritative prediction that will affect large urban areas. When this will be possible depends to a large extent on the support and effort devoted to this problem. In any case, the time is at hand to alert public officials, government agencies, and the public to the fact that a truly useful prediction capability is a real possibility within the foreseeable future. The basic and applied research done in this field now and in the future must be bold yet tempered with wisdom, to assure that society can benefit at the earliest time while avoiding premature overreaction. The benefits to society from accurate earthquake prediction will be substantial in the saving of lives and of property. It has been esti- mated that knowledge of an impending great earthquake, a year or more in

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advance, could result in a large reduction in losses. The savings would result from measures taken to strengthen buildings and their contents, reduce the fire hazard, increase dam safety, enhance nuclear power- plant safety, and the like. For still-shorter-term predictions (e.g., one week), substantial savings of lives would result from temporary measures such as the evacuation of dangerous buildings and the mobiliza- tion of emergency forces. Permanent measures to reduce earthquake hazards, such as better en- gineering design, improved land-use planning, and upgraded building codes and construction practices, will continue to be needed even though earthquake predictions may eventually become completely reliable. There are serious uncertainties concerning community response to a prediction and concerning the impact of an incorrect prediction. These are cur- rently under study by other groups. This report by the Panel on Earthquake Prediction of the Committee on Seismology presents a brief resume of the scientific bases for earth- quake prediction, a summary of current status, and a statement of out- look. Appendixes A and B review in some detail the background and progress of prediction studies in the United States, the Soviet Union, Japan, and the People's Republic of China.