Amy Luddy
November 8, 2001
Coastal Management
Japan’s Tsunami Management
Tsunami, meaning harbor wave in Japanese, is described to be a huge wave
caused by an undersea earthquake or volcanic eruption. Tsunamis have occurred in Japan
on a regular basis throughout history causing them to be inbeded in the Japanese culture.
A tsunami is actually a series of shallow water waves, which are usually caused
by earthquakes, but can also be caused by submarine landslides, eruption of coastal and
island volcanoes, and occasionally, the impacts of meteorites into the ocean. Shallow
water waves are described as having a small water depth to wavelength ratio. The period
between wave peaks is ten minutes to two hours with a wavelength in excess of 300
miles. Comparatively, a wind- generated wave has a period of five to twenty seconds and
a wavelength of 100 to 200 meters. A tsunami’s speed can exceed 1,000 kilometer per
hour. To calculate a tsunami’s speed, compute the square root of the product:
acceleration of gravity times the depth of the water. When a tsunami is out at sea, it is
usually two to three meters in height and cannot be felt aboard ships in deep water. As the
tsunami moves into shallow seas it loses speed and begins to increase in height. The
tsunami can reach thirty to fifty meters high as it enters shallow seas along the coast. The
rate at which these waves lose energy is inversely proportional to its wavelength. This is
why they can travel so far and still be powerful.
Tsunamis hit in several intervals, where the first wave is not necessarily the
largest. Many deaths are accountable to the misconceptions that a tsunami is only one
wave or that the first wave of a tsunami is the largest. The majority of tsunamis occur in
the Pacific Ocean because of the subduction zones associated with this area. Areas at risk
are less than fifty feet above sea level and within one mile of the shoreline. The contour
of the ocean floor and coast can affect the shape and direction of a tsunami. An example
of this is the Yamato Ridge in the Sea of Japan, which is deeper than the rest of the sea.
Japan is a country that is constantly threatened by tsunamis. In the last 500 years all of
the coasts of Japan have been hit by a tsunami. Two major tsunamis that have occurred
in Japan were the Chile earthquake and tsunami and the 1993 Hokkaido tsunami.
On May 22, 1960, Chile experienced the largest earthquake ever recorded with a
magnitude of 9.5. The fault was ruptured releasing a buildup of energy. The South
American plate moved sixty feet over the subducting Nazca plate. Tsunami hit Chile and
then reversed across the Pacific Ocean, traveling 17,000 km to hit Japan. Waves reached
14 feet in height and 122 fatalities were recorded (Surviving a Tunami – Lessons from
Chile, Hawaii, and Japan, pp 2-3).
A 7.8 Magnitude earthquake occurred off the West coast of Hokkaido in the Sea
of Japan, causing a tsunami to hit Hokkaido and surrounding shores of Japan. The large
waves caused destruction of the sea wall in Hokkaido and rampant fires. Water levels
were up to nine meters along the coast. The death toll reached a tragic 200 and was
blamed partly on the misbelief that tsunami wouldn’t occur in the Sea of Japan, causing
the first tsunami warning to be issued after the first wave had already hit (The Hokkaido
Nansei-Oki Earthquake, pp. 1-2).
The International Tsunami Information Center (ITIC), located in Honolulu,
Hawaii, was founded in 1965. Its mission is to reduce the risk of lives and property to
those whose coasts that are threatened by tsunamis. The ITIC promotes regional
cooperation and contributes to scientific and technical training of tsunami experts. It
works to improve tsunami warning systems by monitoring activities, working closely
with other regional national centers in monitoring seismological stations, tidal stations,
and instruments around the Pacific Ocean to evaluate earthquakes that could potentially
cause tsunamis. Unfortunately, the current technology available is not able to accurately
predict tsunamis caused by other events (Tsunami Warning System in the Pacific).
Studies of those who survive tsunamis show that education and early warnings are
the best defense against loss of life. Some of these procedures are: heed natural warnings
such as earthquakes and rapid rise or fall in sea level. Don’t stay in low-lying areas after
a strong earthquake has been felt and listen for possible tsunami warnings. Leave behind
belongings and do not return until you are advised that it is safe to return. Never go to
the shore to watch a tsunami. If you see it you are too close to escape because of the
wave’s rapid speed. Don’t count on roads being accessible and expect earthquakes to
lower coastal land. Some last resort tips from survivors include climbing trees, climbing
onto something that floats, and going upstairs in a building. The three major reasons
people become victims to tsunamis are that they do not evacuate, they evacuate too late,
or they evacuate but return too early.
Japan has various policies to try to lessen the impact tsunamis have on its coastal
areas. The country’s newest prediction method involves a fleet of buoys moored out in
the ocean which are linked to Global Positioning Systems that monitor the change in
vertical position of buoys to just fractions of an inch. They also have meteorological
instruments that send information to forecasting center where computers are used to find
the epicenter and magnitude of earthquakes. From this data, a prediction is made on if a
tsunami will occur and how large it is expected to be. Most coastal towns have sirens to
warn the community of the inevitable danger. Once a year many coastal areas conduct
preparedness drills where they practice swift evacuation (Tsunamis. How Occur?! How
Protect?!).
The San Rico coast is the area in Japan that is most prone to tsunamis because of
its v-shaped valleys. Seawalls and breakwaters are used to protect this area. Breakwaters
close off the bay except for a 200 meter opening for boats. It is thought that the
breakwater is able to prevent tsunami waves of up to six meters from entering the bay.
Some villages have moved to higher ground since tsunamis in the past. However, lapses
in time between tsunamis, allow people to forget their devastation and coastal
development begins to increase.
This lapse in memory is a major component in deaths caused by tsunamis.
Education is a key ingredient in saving lives. In Karakuwa there is a tsunami simulation
hall where you can experience what a real tsunami would be like. Places such as this are
constant reminders to the community of the looming danger tsunamis present. The
national television network in Japan also makes various educational videos on the topic.
number of educational videos through their national television network (Tsunamis. How
occur?! How Protect?!).
Bibliography
1. Tsunami. How occur?! How protect?! International Tsunami Information Center,
1995.
2. Atwater, Brian F., Cisternas V., Marco, Dudley, Walter C., Hendley, James W.,
Stauffer, Peter H. U.S. Geological Survey. Surviving a Tsunami - lessons from
Chile, Hawaii, and
Japan. Circular 1187 (1999): pp. 1-18.
3. National Oceanic and Atmospheric Administration. The Hokkaido Nansei-Oki
Earthquake July 12, 1993. Circular 1143-A11-027 (1997): pp. 1-7.
4. The Tsunami Warning System in the Pacific. Intergovernmental Oceanographic
Commission. 28 September 2001
<http://ioc.unesco.org.iocweb/activities/tsunami.htm>