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that erupt in volcanoes. The plate motions accumulate stresses in the brittle part
of the lithosphere, releasing strain energy through sudden failures on faults,
causing earthquakes. Plate tectonics pushes up mountains and creates other
topographic features, which release gravitational energy in the form of landslides
and avalanches. When major landslides and earthquakes occur under the ocean,
some of the potential energy that is released can propagate in the form of huge
sea waves (tsunamis), inundating coastlines thousands of miles away.
Floods, droughts, severe storms, volcanic eruptions, earthquakes, landslides,
and tsunamis compose a catalog of natural disasters that have wreaked destruction
since the beginning of civilization. Only recently, however, has the changing
nature of these threats been recognized. The process of urbanization begun in the
Industrial Revolution continues apace; in 1950, only 3 out of 10 people lived in
urban areas, while by 2030 this fraction will nearly double. As populations and
the fragile infrastructures on which they depend concentrate in large urban areas,
the risks of natural hazards, especially the economic risks, grow correspondingly.
With regard to seismic hazard, Japan is fairly well prepared for earthquakes. Yet
the modest-sized earthquake (magnitude 6.9) that struck Kobe on January 18,
1995, killed 5500 people and resulted in an economic loss of nearly $200 billion.
According to one recent study, a repeat of the great 1923 Kanto earthquake
(magnitude 7.9) would devastate modern Tokyo: the direct economic losses
would total a staggering $2.1 trillion to 3.3 trillion, equivalent to 44-70% of
Japan's annual gross domestic product. 9 An event of this magnitude clearly
would have an impact extending well beyond any one nation, affecting the entire
global economy and thereby directly influencing the welfare and security of the
United States.
On a worldwide basis, the problem of urban hazards is further amplified by
the fact that the most severe natural disasters—earthquakes, hurricanes,
typhoons, and volcanic eruptions—tend to be concentrated in low-latitude,
coastal regions, where ambient environmental conditions support large
populations and the current economic development is most intense. 10
9 Risk Management Solutions, Inc., Menlo Park, California, What If the 1923
Earthquake Strikes Again? A Five-Prefecture Tokyo Region Scenario, 97 pp., November
1995. Another report in the same series estimated that repeat of the 1906 San Francisco
earthquake, also magnitude 7.9, would result in a 3000-8000 deaths and a direct economic
loss of $170 billion to $225 billion (1994 dollars).
10 R. Bilham, in Reduction and Predictability of Natural Disasters, J. Rundle, D.
Turcotte, and W. Klein, eds., Santa Fe Institute Studies in the Science of Complexity, Vol.
XXV, Addison-Wesley, pp. 19-31, 1996. Earthquakes and volcanoes occur predominately
on or near the boundaries of the tectonic plates; the most active plate boundaries are
concentrated at low latitudes, probably because the Earth's principal moment of inertia is
determined by convective upwellings and downwellings.
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