One of the most frightening and destructive phenomena of nature is a severe earthquake and its aftereffects. Catas- trophic earthquakes account for 60% of worldwide casu- alties associated with natural disasters. Economic damage from earthquakes is increasing, even in technologically ad- vanced countries with some level of seismic zonation, as shown by the 1989 magnitude 6.9 Loma Prieta, CA (more than $6 billion), 1994 magnitude 6.7 Northridge, CA (more than $25 billion), 1995 magnitude 6.8 Kobe, Japan
(more than $100 billion), and 1999 magnitude 7.4 Turkey (more than 1.5% of the GNP of Turkey) earthquakes. Vulnerability to natural disasters increases with urban- ization and development of associated support systems (reservoirs, power plants, etc.). The growth of megaci- ties in seismically active regions around the world often includes the construction of seismically unsafe buildings and infrastructures, due to an insufficient knowledge of existing seismic hazard. Mitigation of the effects of earth- quakes, including the loss of life, property damage, and social and economic disruption, depends on reliable esti- mates of seismic hazard. National, state, and local govern- ments; engineers; planners; emergency response organi- zations; builders; corporations; scientists; and the general public require seismic hazard estimates for land use plan- ning, improved building design and construction (includ- ing adoption of building construction codes), emergency response preparedness plans, economic forecasts, housing and employment decisions, and many more types of risk mitigation.