Geography Reference
In-Depth Information
of buildings such as these are located in seismically suspect regions in developing countries. Each is
a potential tragedy waiting to happen.
In contrast, superior construction is much more predominant in wealthier settings. Skeletal steel is
much more common, as is implementation of the latest thinking regarding earthquake-resistant build-
ings. In that regard, an ideal model is the way a tree bends in a strong wind, absorbing the punch.
The implication is to build structures that bend with the punch — or rather, sway with the earthquake.
This is done by attaching girders in a way that produces a skeleton that is rather like your own — it
bends.
Building codes in earthquake-prone areas of the United States, and in other parts of the world, now
mandate this kind of construction. And these laws clearly are having their desired effect. But modern
construction is costly — much more so than the traditional masonry that continues to dominate much
of the earthquake-prone world as a matter of tradition and inability to afford the state-of-the-art al-
ternative.
Tsunamis
When earthquakes occur under the ocean, the sea floor may rise or fall by a few feet over an
area hundreds of miles on a side. This happens in a matter of seconds. With the sea surface
suddenly a few feet too high or too low over a huge area, enormous volumes of water are set
in motion to bring the sea surface back to level. This produces a long, low wave that moves
out across the ocean in every direction at speeds that may exceed 400 miles per hour. In the
open ocean the wave is less than 3 feet high, but may be 300 miles across. Although the wave
is moving over 400 miles per hour, because the wave is so broad, the 3-foot rise and fall takes
10 or 20 minutes and if it passed under your ship at sea it would not even ripple the surface of
your martini. You wouldn't even notice it. But as the wave encounters shallow coastal waters,
it slows down and grows enormously in height, manifesting itself as a
tsunami
, or large “tid-
al wave.” The size of the wave is directly related to the magnitude of the earthquake. Strong
quakes may produce waves 30 to 50 feet in height, and 100-feet monster waves are not un-
known.
Naturally, the destructive potential of these waves in regard to coastal settlements is substantial.
Given the seismically and volcanically active plate boundaries that border the Pacific Ocean, more
tsunamis affect that ocean's shores than any other (see Figure 6-4). Japan has been one of the most
affected regions, which explains why the word “tsunami” is of Japanese origin.
