Earthquakes

by CBBC website

Why do earthquakes happen?

Although the ground we walk on seems solid, the earth is actually made up of huge pieces of flat rock called tectonic plates. These move very slowly, and where they meet is called a fault. When the plates rub together, the movement forces waves of energy to come to the earth's surface. This causes tremors and shakes - and this is what causes earthquakes.

Why are earthquakes dangerous?

Earthquakes can be very dangerous, if you are in the wrong place. They can make buildings fall down and set off landslides, as well as having many other deadly effects. An earthquake which occurs on the seafloor can push water upwards and create massive waves called tsunamis. These waves can reach speeds of up to 500 kilometres per hour and cause massive devastation to anything in their path. Earthquakes are measured on the Richter scale. The higher the number on the scale, the more powerful the quake. The more powerful a quake is, the more damage it can cause. Earthquakes have killed hundreds of thousands of people even though scientists are able to make buildings much safer than in the past. Unfortunately many quakes happen in parts of the world where people can't afford to spend lots of money on safety measures.

Did you know there are over a million earthquakes each year in all parts of the world? But we don't notice most of them because they are so small. Britain doesn't have a history of devastating earthquakes, but there are 200 to 250 on average a year, and about 30 of those can be felt.

Have there been serious earthquakes recently?

In recent years, there have been some really big earthquakes:

Japan earthquake and tsunami, March 2011

A massive 8.9 magnitude earthquake and tsunami struck Japan killing over 15,000 people. The tsunami damaged a nuclear plant in Fukushima in the north of the country which later suffered several explosions causing people living nearby to flee their homes.

Christchurch, New Zealand earthquake, February 2011

Over 150 people were killed when a 6.3 magnitude quake hit Christchurch in New Zealand. The tremors caused the city's cathedral to collapse and was the country's worst natural disaster in 80 years.

Sumatra earthquake, October 2010

A big 7.6 magnitude earthquake hit off the coast of the Indonesian island of Sumatra. Over 700 people were killed. The quake hit just a few hours after an earlier one in the area caused a tsunami that killed 100 islanders.

Haiti earthquake, January 2010

A strong earthquake hit Haiti in the Caribbean. It devastated the country, and it's thought between 100,000 and 200,000 people died. Hundreds of buildings were demolished and 1.5 million people were made homeless.

Why is it dangerous after an earthquake?

Earthquakes are often followed by aftershocks, causing even more damage to already weakened buildings and roads. Land, especially hills, can also be damaged by earthquakes and result in devastating landslides and mudslides.

What is an aftershock?

• It's basically a smaller earthquake that happens after the main quake, in the same area.

• If it registers higher on the Richter scale than the first quake, it's renamed as the main earthquake and the original main quake becomes known as a foreshock.

• Aftershocks can happen for up to two years after the original earthquake, losing power over time.

The risk of disease

In the chaos that can occur after an earthquake, sometimes electricity and fresh water can be lost. When there's no fresh water, this can lead to the spread of diseases.

Even getting hold of food and basic supplies can be difficult after an earthquake, because roads and other transport links can be destroyed.

The long-term effects of earthquakes can be felt for years afterwards.