Case Study: Earthquakes
The rocks inside the Earth are constantly moving due to huge pressures inside. Sometimes the rock becomes locked in place, and the pressure continues to build up. Eventually the rock breaks or changes shape and releases energy in the form of waves.
All waves produces by earthquakes are called seismic waves (seismos mean earthquake in Greek). These waves carry energy through the Earth. |
There are 3 main types of seismic waves;
P Waves (Primary waves): These are longitudinal waves which travel the fastest. They are made up of compressions and rarefactions of rock inside the Earth which compress and expand the ground. S Waves (Secondary waves): These are transverse waves which shake the ground up and down and side to side. Surface Waves: When P and S Waves reach the Earths surface, they create surface waves. These are a combination of longitudinal and transverse waves which travel along the surface of a medium. They move more slowly than P and S waves but potentially cause the most damage as they make the surface roll up and down and side to side. |
When an earthquake occurs under the ocean the surface waves can cause Tsunamis. These can travel thousands of kilometres across the ocean. In the deep ocean they may only be 1 metre or less. However, when they approach shallower water, the slow down and form giant waves - The 2004 Indian Ocean tsunami killed more than 230,000 people and resulted in 100 billion worth of property damage.
In 2011 a 9.0 magnitude earthquake struck just 70km of the North East coast of Japan. It was the biggest in recorded history for the country and one of the 5 biggest in world history. It created a devastating tsunami which was up to 40m high in some places, and which travelled inland as much as 10km. It resulted in almost 20,000 deaths and also led to the partial meltdown of a number of nuclear reactors in the area.
In 2011 a 9.0 magnitude earthquake struck just 70km of the North East coast of Japan. It was the biggest in recorded history for the country and one of the 5 biggest in world history. It created a devastating tsunami which was up to 40m high in some places, and which travelled inland as much as 10km. It resulted in almost 20,000 deaths and also led to the partial meltdown of a number of nuclear reactors in the area.