Geoscience Reference
In-Depth Information
The tsunami resulted from sudden land displacement
of 2-4 m along the fault during the earthquakes.
Within 15 minutes of the faulting, three large waves
devastated coastal towns in Chile, where over 1700
people lost their lives. The arrival of the first wave was
predicted at Hilo, Hawaii, five hours in advance to an
accuracy of one minute. Unfortunately, 61 people,
mainly sightseers, were killed as the wave hammered
the Hawaiian Islands. When the wave reached Japan
24 hours later, it still had enough energy to reach a
height of 3.5-6 m along the eastern coastline. Five
thousand homes were washed away, hundreds of ships
sank and 190 people lost their lives. In Hawaii, this
event illustrated the folly of some humans in the face
of disaster. Despite plenty of warning, only 33 per cent
of the residents evacuated the affected area in Hilo.
Over 50 per cent evacuated only after the first wave
arrived, and 15 per cent stayed behind even after large
waves had beached. Many of those killed were spec-
tators who went back to see the action of a tsunami
hitting the coast.
Warning System, in one of the most successful disaster
mitigation programs in existence. The countries
involved include Canada, the United States and its
dependencies, Mexico, Guatemala, Nicaragua,
Colombia, Ecuador, Peru, Chile, Tahiti, Cook Islands,
Western Samoa, Fiji, New Caledonia, New Zealand,
Australia, Indonesia, Philippines, Hong Kong, People's
Republic of China, Taiwan, Democratic People's
Republic of Korea, Republic of Korea, Japan and the
Russian Federation. An additional ten countries or
dependencies receive PTWC warnings. Many of the
primary countries also operate national tsunami
warning centers, providing warning services for their
local area.
The Pacific Tsunami Warning System relies on
any earthquake 6.5 or greater on the Richter scale reg-
istering on one of thirty-one seismographs outside the
shadow zones of any P- or S-waves originating in
the Pacific region (Figure 10.17). These stations are
operated by the Center itself, the West Coast and
Alaskan Tsunami Warning Center, the United States
Geological Survey's National Earthquake Information
Center, and various international agencies. Once a
suspect earthquake has been detected, information is
relayed to Honolulu where requests for fluctuations in
sea level on tide gauges are issued to member countries
operating sixty tide gauges scattered throughout the
Pacific. These gauges can be polled in real time so that
warnings can be distributed to one hundred dissemina-
tion points with three hours' advanced notice of the
arrival of a tsunami. For any earthquake with a surface
magnitude of 7 or larger, the warnings are distributed
to local, state, national, and international centers.
Administrators, in turn, disseminate this information
to the public, generally over commercial radio and
television channels. The National Oceanic and Atmos-
pheric Administration (NOAA) Weather Radio system
provides direct broadcast of tsunami information to the
public via very high frequency (VHF) transmission.
The US Coast Guard also broadcasts urgent marine
warnings on medium frequency (MF) and VHF
marine radios. Once a significant tsunami has been
detected, its path is then monitored to obtain infor-
mation on wave periods and heights. These data are then
used to define travel paths using refraction-diffraction
diagrams calculated beforehand for any possible tsunami
originating in any part of the Pacific region.
The United States supplements these warnings
using six seabed transducers that have been installed
Pred
iction in the Pacific region
(Sokolowski, 1999; Bryant, 2001; International Tsunami
Information Center, 2004)
The most devastating ocean-wide tsunami of the past
two centuries have occurred in the Pacific Ocean.
Following the Alaskan tsunami of 1946, the United
States government established a tsunami warning
system in the Pacific Ocean under the auspices of
the Seismic Sea Wave Warning System. In 1948, this
system evolved into the Pacific Tsunami Warning
Center (PTWC). Warnings were initially issued for the
United States and Hawaiian areas; but, following
the 1960 Chilean earthquake, the scheme was extended
to all countries bordering the Pacific Ocean. Until
1960, Japan had its own warning network, believing at
the time that all tsunami affecting Japan originated
locally. The 1960 Chilean tsunami proved that large
submarine earthquakes in the Pacific Ocean region
could spread tsunami ocean-wide. The Pacific Tsunami
Warning System was significantly tested following the
Alaskan earthquake of 1964. Within forty-six minutes
of that earthquake, a Pacific-wide tsunami warning was
issued. This earthquake also precipitated the need for
further international cooperation on tsunami warning
in the Pacific. The United States National Weather
Service currently maintains the Center. Currently,
twenty-five countries cooperate in the Pacific Tsunami
