A tsunami is a powerful and destructive wave. Underwater
earthquake, volcano eruption or underwater landslide and
activities of land can cause tsunamis.
When the eartuquake occurs, the seabed strata broke and
some of the strata suddenly rose or sank, resulting in
a violent shaking of the entire water layer from the bottom
of the sea. Such vibration is different from usual waves.
Waves generally tend to rise and fall only near the surface
of the sea and the amplitude decreases rapidely with the depth
of the water. However, the shaking of water caused by earthquake
is vibration from the bottom of the sea to the surface,
where the energy is amazing.
Tsunami waves are very large and can spread thousands of kilometers
with small loss of energy. After a shock, the shock waves spread
far away from the sea, just as the pebbles fall into the shallow pool.
The waves caused by earthquake are different from those
in the sea. General waves fluctuate only at a certain depth,
while the fluctuations caused by earthquake are of the
entire water layer from bottom to surface.
A destructive earthquake and tsunami only occur
when a vertical fault occures and the magnitude of earthquake
exceeds 6.5. The velocity of a tsunami is proportional to
the depth of its migration. In Pacific Ocean, tsunamis
typically travel between two or three hundred kilometers
per hour to over 1000 meters. Tsunamis do not cause disasters
in the deep ocean and it is even difficulf for sailing ships to
perceive this fluctuation. When a tsunami happens,
it is safer to be outside.
Once the tsunami enters into the continental shelf, due to
a sharp decrease in depth and the wave height increases dramatically
and huge waves will be produced, which can be devastating.