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management, hazard-resistant construction, and other anticipatory measures reduce the world's vulnerability to natural hazards. Strategies for avoiding the impacts of natural hazards and lines of applied research and tech- nology that can dramatically reduce the frequency of catastrophes are reviewed in the following sections. HAZARD AND RISK ASSESSMENT How does a community begin to reduce the impacts of natural disasters? The first step is to determine the types of hazards likely to occur, their frequency, characteristics, and conse- quences. Experience is a good teacher, but changes in population patterns, physical charac- teristics of structures, and economic development over the past century suggest that relying on experience alone is inadequate for judging vul- nerability. Risk assessments of the nature, extent, and consequences of natural hazards lie at the core of adopting efficient and economic actions to lessen catastrophe potential. There is a natural competi- tion for resources between investment in hazard reduction measures for the future and use of capital and labor that will yield current income or improve the quality of life immediately. Evaluat- ing risks can help in estimating the likely level of hazard and in determining the economic and social costs associated with various levels of investment in hazard reduction. Assessment has three essential features: ~ Determination of the hazard. This is often described in terms of hazard or intensity maps of the maximum event likely to occur, frequency of the event (for example, demarcation of a 50- or IOO-year flood area), and the numerical values of design parameters required to withstand the forces of a natural hazard (for example, the level of ground motion a structure must accommodate). . Determination of the vulnerability of the structures and facilities exposed. This includes individual structures and networks of interacting structures, such as water supply and distribution pipelines, and social institutions, such as fire and hospital services. . Determination of the significance of the im- pacts. This determination must: differentiate 21 among saving lives, protecting property, and preserving essential community functions; com- pare the benefits of avoiding a disaster with those of investing in other economic and social func- tions; recognize the different roles of structures and institutions in emergency response and recov- ery activities; and recognize the different and possibly conflicting goals and values of individu- als and institutions within a community. Knowing that a major natural hazard may occur is not sufficient in itself to cause action. California, where nine major earthquakes oc- curred in the last 150 years (including four great earthquakes), did not begin a comprehensive earthquake safety program until the seismic threat was clearly understood economically and politically. This understanding came about when the office of the President of the United States determined the scale of the impact of a cata- strophic earthquake on the local and national economy. The specter of a staggering $100 billion loss - with attendant loss of life and damage to industrial productivity - prompted local, state, and federal governments to begin a concerted effort to prepare for the occurrence of great earthquakes. The kinds of information that nations require to develop and adopt a catastrophe avoidance plan do not vary much from country to country, but the strategies appropriate to different coun- tries obviously do. Formulating goals and taking action depend almost entirely upon social organi- zation and on the willingness of the public to accept the consequences of its actions. Some individuals and groups will choose not to act because of an incorrect understanding of what they are to do, a lack of education in how to do it, or a vested interest in doing something else. The economic, social, and institutional dimensions of a community may well determine what is appro- priate as well as what is possible. DISASTER PREPAREDNESS Disaster preparedness is the detailed planning for prompt and efficient response once a hazard occurs; it is the first step in adopting an antic- ipatory approach to natural hazards. This com- prehensive effort includes public education and awareness campaigns, provision for issuing warn-