Geoscience Reference
In-Depth Information
Introduction
THE TSUNAMI THREAT IN THE UNITED STATES
The 2004 Indian Ocean tsunami resulted in catastrophic losses of life and property and
demonstrated how destructive tsunamis can be. More than 200,000 people died, with most
occurring in Indonesia, which was near the tsunami source, but deaths were also reported in
countries as far away as Somalia. Recently, the Samoan (September 2009) and Chilean (February
2010) tsunamis reminded the world of how quickly a tsunami can move onshore and destroy
lives. In comparison to extreme weather—such as loods, hurricanes, or tornadoes—tsunamis
have caused comparatively few fatalities in the United States over the past 200 years. Modern
records kept since 1800 tally less than 800 lives lost due to tsunamis in the United States and
territories.
1
In 1960, a magnitude 9.5 Chilean earthquake generated tsunami waves that killed
61 people and caused $24 million in property damage in Hilo, Hawaii (Eaton et al., 1961). The
1964 Good Friday earthquake in Alaska generated a tsunami that devastated local Alaskan com-
munities and inundated distant communities as far south as Crescent City, California.
Earlier tsunamis—yet to be repeated in modern times—include tsunami waves of North
American origin in the year 1700 that caused looding and damage as far away as Japan. Paleo-
records indicate that the Cascadia subduction zone off the Washington, Oregon, and northern
California coasts has repeatedly generated potentially catastrophic tsunamis (Atwater et al.,
2005). Because of the relative infrequency of catastrophic tsunamis in recent U.S. history, mobi-
lizing the required resources to maintain the nation's warning and preparedness capabilities is
challenging.
Tsunamis are caused by a variety of geological processes, such as earthquakes, subaerial
and submarine landslides, volcanic eruptions, or very rarely from meteorite impacts (Box 1.1).
However, it takes a large event (e.g., typically an earthquake of magnitude greater than 7.0)
to generate a damaging tsunami. Therefore, determining the likelihood of future tsunamis for
U.S. coastal communities requires an understanding of the likelihood of reoccurrence of such
geological processes, the likely magnitude of such events, and the location of the sources (see
Chapter 3 for additional details). Because most tsunamis result from earthquakes, the tsunami
hazard is high along U.S. shores that adjoin boundaries between tectonic plates, particularly
along the subduction zones of Alaska, the Paciic Northwest, the Caribbean, and the Marianas
(Figure 1.1). However, U.S. shores are also exposed to tsunamis generated far from them. For
example, Hawaii has been struck by tsunamis that have been generated by earthquakes off
the coasts of South America, Russia, and Alaska (Cox and Mink, 1963). Submarine landslides,
1
http://www.ngdc.noaa.gov.
