EPSC201 - Lecture 6 Notes
Tsunamis – huge waves caused by earthquakes
Japan Earthquake (2011):
The pacific plate is plunging under Asia, which causes lots of earthquakes at the interface of the Asian
and pacific plates. Its an ongoing process. The movement is jerky, never smooth, which causes tension to
build up, and eventually overcomes friction. The net result is an earthquake. The longer time in between
earthquakes, the greater in magnitude they will be.
Disturbances of the plates on the ocean floor will cause waves. Not just one wave, but possibly many. It
took nine hours from the wave from Japan to hit North America. It takes 13 hours by plane, which means
the waves are traveling faster then the plane (over 1000km/h). Extremely fast when moving in the open
In the open ocean, you would hardly notice a wave. The picture below show the height of the waves in
the open ocean. Closer to land, the wave is
amplified. The wave slows down from 1000
km/h to about 60 km/h but it is much greater in
amplitude. Fisherman will notice a tiny wave
and not think much of it, and return back to
shore to find devastation.
The incoming wave is of average height of 11
meters at shore. However, it could be much
higher then this, for example 30 meters. The
devastation is enormous. Many lives are usually
lost. Coastal countries are extremely
In Japan’s case, the added problem was that
Japan is a nuclear dependent country. The
Fukushima reactor was close to the coast,
and there was a meltdown. In a hundred meter
radius, people were affected by the radiation. A
large number of people were affected by
radiation sickness or poisoning. There was a
slow response due the tsunami occurring
9.3 Richter scale earthquake in the South
Pacific. Large number of people killed in Sri
Lanka and Indonesia. Happened on Boxing
Day, 2004. 50000 killed in Sri Lanka and
200000 in Indonesia. The pacific plate is again
diving under the Asian plate, causing
earthquakes. Major damage and loss of life,
over a large area. Thailand was also affected.
The water from the beaches goes out to sea.
The water recedes out very far. This is a sign
that a tsunami is incoming. If people knew, they
would have more time to get to safety. A 13-
year-old British schoolgirl was on vacation in
Thailand, and had learned about tsunamis in
geography. She recognized that a tsunami was
incoming because the rapid recession of water
out to sea. This girl saved about 300 lives.
What about warning systems? Education – first line of defense. You have several minutes after the water recedes before the incoming
wave(s) hit shore.
Banda Aceh took the most damage. This change
occurred in a manner of minutes.
By looking at plate movement and past
earthquakes, one can predict where the next
earthquake will occur. Sea floor displacement
propagates tsunami waves.
Sri Lanka had about a 1.5 hours before the
waves hit. If a warning system was in place,
50000 lives could have been saved.
Stuck area will eventually slip and release all the
energy at once. Will cause sea floor to bounce up rapidly, causing tsunami waves. Tsunamis in open water have a wavelength of 100,000 meters and are small in amplitude. As they come
into shallow water, wavelength shortens, and amplitude increases. As the wave gets pushed up, it slows
down, which causes the waves behind it to catch up. The waves pile up, and will hit shore in succession.
Sri Lanka had approx 2 hours. Std – standard time in
hours The coast of East Africa got hit several hours
Well developed countries have good early warning
systems. The West coast of North America is
earthquake prone. The small island on the coast of
B.C. provide a barrier for the mainland (example –
Vancouver Island shelters Vancouver City)
Within seconds, people will know a tsunami is
imminent. Its better to error on the side of caution.
Indian Ocean did not have an early warning
system. In the last year, one has finally been
installed, due to recent tsunamis and awareness.
The pacific ocean has had a warning system for a
Earthquakes Are A