The Earth's crust

The Earth's crust is not just one huge rock 'skin'. It actually consists of 20 pieces called 'tectonic plates'. Earth's hills and mountains were formed as these plates bumped into each other forcing the land to rise. 

Causes of an earthquake

A building damaged by an earthquake. Getty Images

A building damaged by an earthquake. Getty Images

The tectonic plates are always moving. They usually slide past each other very very slowly, and the movement is not noticeable. If the edges of the plates get stuck, rocks bend and split, causing a fault, or a weakness, in the Earth's crust. Where the plates are stuck, pressure builds up, there is a violent release of energy and the Earth shakes. 

Most earthquakes occur under the sea. There are about 3000 earthquakes every day, many are so small that they are not noticed. Volcanoes that are erupting can also cause earthquakes.

A road buckled and broken by an earthquake. ©iStock

A road buckled and broken by an earthquake. ©iStock

Large earthquakes shake the ground and destroy buildings. People get killed or injured, and gas and water pipes underground are twisted and burst. Railway lines get buckled by the earthquake.

Measuring the strength of an earthquake

Scientists use instruments called seismographs (say size-mu-graphs) to measure the strength of tremors and earthquakes.

The Richter Scale, named after Dr. Charles F. Richter of the California Institute of Technology, is the best known scale for measuring the magnitude of earthquakes.The Richter Scale is the measure of the tremors.

The Modified Mercalli Scale measures the damage caused by an earthquake.

Earthquakes under the sea can start a tsunami that travels towards the coasts of nearby islands or countries, threatening the people who live there.




Read about the Richter Scale and the Modified Mercalli Scale:

Read the kidcyber page:

  • Tsunami(say tsoo-nah-me)

  • A tsunami is a huge wave.

  • It is causes by an earthquake.

  • Tsunami is a Japanese meaning 'harbour wave

What is a tsunami?

A tsunami is a huge, long wave that comes suddenly and often without warning.

What causes a tsunami?

When an earthquake or volcano occurs, the vibrations cause a drop in the sea bed and water floods into the gap. When the gap is full, water rushes back in the opposite direction and creates a long wave.

Movement of tsunami

At sea, a tsunami is only slightly higher than other waves. A tsunami moves at great speed, up to 800 km per hour. As it moves nearer to the coast it slows down and can become higher than 50 metres.


By the time the wave reaches the land, it is a high wall of moving water that crashes onto the land. The volume of water and the force of its impact causes huge devastation. It then draws back into the sea again, dragging with it anything in its path.

Word meaning

'Tsunami' is a Japanese meaning 'harbour wave'. They used to be called 'tidal waves', but this is an inaccurate term as they are not caused by tides.

Watch a video of an earthquake that caused a devastating tsunami in Japan in 2011

Earthquake and Tsunami, Japan, 2011