Earthquake Information:

22. How does a tsunami propagate?

A tsunami is referred to as the long waves from its occurring area propagating out in each direction. Its speed v depends on the ocean depth, and the equation is as follows:

v = gh

h: depth of the sea   g: acceleration of gravity

Generally, in the deep and broad ocean, its propagation velocity is approximately 500 to 1,000 kilometers per hour. The wave height usually does not surpass 30 to 60 centimeters, which will not cause any problem to ships at sea level. However, when the waves approach the coast, these waves will be affected by the local littoral landforms and the ocean floor. Hence, the forward velocity of the waves is reduced, resulting in the stack phenomenon as to form huge waves. It causes major destruction to the coastal area and also the loss of life and property.

21. What is the cause of a tsunami?  23. Are all tsunamis disastrous?