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Seismic risk will increase through the remainder of this century, not because the incidence of damaging earthquakes is changing, but rather because our exposure to them is growing. The human population will reach more than 9 billion by AD 2050, about one-third larger than its current 6.8 billion, and much of this growth will occur in areas that experience damaging earthquakes. Population growth will be accompanied by continuing urbanization, an inevitability that will see well over half the world's population living in cities by the middle of the century. With urbanization will come a rapid increase in the number of megacities, many of which will be located in earthquake-prone areas, along with greater concentrations of infrastructure, human capital, and national wealth in cities. A large earthquake in a growing city such as Tokyo, Los Angeles, or Istanbul would be a national disaster with global economic fallout. The global economic consequence of natural disasters is a developing issue, first illustrated by the Kobe earthquake in 1995 and Hurricane Katrina in 2005.
Consideration of seismic risk must distinguish risk to human life from economic risk. Major improvements in earthquake engineering in the U.S., Canada, Japan, and other countries have reduced the risk to human life to a very low level. Large earthquakes in California in 1989 (Loma Prieta) and 1994 (Northridge), for example, each caused less than 70 fatalities. However, no such improvements have happened in earthquake-prone developing countries, consequently the risk to human life there is growing. In contrast, economic risk is increasing in both developed and developing countries due to the aforementioned trends in urbanization and concentration of economic wealth in cities. The Loma Prieta and Northridge earthquakes caused a total of $20-25 billion damage, yet were by no means the largest earthquakes that are possible in San Francisco and Los Angeles. Earthquakes causing more than $100 billion damage are likely in coming years unless the existing stock of older buildings in our cities is replaced with buildings capable of withstanding high ground accelerations without significant damage.
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