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CHAPTER 4 Major Natural Hazards The nature of each major natural hazard is distinct, as are the challenges associated with reducing its impacts. This chapter traces the unique character of the major hazards and sug- gests IDNHR projects to address each one. These project lists are by no means exhaustive and are intended only to indicate the possible scope of IDNHR activities. The chapter also explores the socioeconomic aspects of hazard reduction and the special challenges of coping with multiple hazards. EARTHQUAKES An earthquake - a sudden motion of the earth caused by an abrupt release of slowly accumulat- ing stress - is a potent natural hazard. Dangers associated with earthquakes include the phe- nomena of ground shaking, surface faulting, ground failures, and tsunamis. Although earth- quakes cause less economic loss annually than some other natural hazards, they have the poten- tial for causing great sudden disasters. Within one minute, an earthquake can destroy part or all of a city. Depending upon its location and magnitude, it can damage buildings and homes valued at billions of dollars, cause loss of life and injury to tens of thousands, and totally disrupt a com- munity's social and economic functioning. At least 35 countries face a high probability of loss from earthquakes. Moderate (magnitudes of 6-7) and large (magnitudes of 7-8) earthquakes pose the greatest threat because they are much more frequent than great earthquakes (magni- tudes of 8 and above). For example, a moderate earthquake takes place about once a year in California, but a great earthquake happens only once every 100 years or so. The extent of a disaster wrought by an earth- quake depends upon the magnitude of the earth- quake, its proximity to a city, and the city's preparation to resist an earthquake. In the past 25 years, the two most destructive U.S. earthquakes were in Prince William Sound, Alaska, in March 1964 (magnitude 8.4) and in San Fernando, California, in February 1971 (magnitude 6.5). Damage of about $500 million (1971 dollars) and scores of deaths and injuries resulted from each. Yet the United States has been relatively fortunate. The Tangshan, China, earthquake of July 1976 (magnitude 7.8) destroyed the entire city, leaving more than 250,000 dead. The Mexico earthquake of September 1985 (magnitude 8.1) caused 10,000-20,000 deaths and about $6 billion in damages. The moderate (magnitude 6) earth- quake of 1960 near Agadir, Morocco, caused more than 10,000 deaths in a city of 30,000. The 1908 Messina, Italy, earthquake (magnitude 7.8) killed about 80,000, and the 1923 Tokyo earth- quake (magnitude 9) killed more than 140,000. The main goal of an earthquake hazard reduc- tion program is to preserve lives through the economical rehabilitation of existing structures and the construction of safe new structures. One further goal is to ensure that emergency response, recovery, and redevelopment plans are made to provide continuity of economic, social, and politi- 33