Why do they 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.

Are they 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.

How often do they happen?

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 ones recently?

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

December 2004:
Some 300,000 people are killed
when an earthquake in the Indian Ocean
measuring 9.0 on the Richter scale
sends huge waves called tsunamis
crashing into several Asian countries.

The worst countries affected were Indonesia,
Sri Lanka, India and Thailand.
 

December 2003:
Over 50,000 people are killed in a quake in Iran,
which measured 6.3 on the Richter scale.
 

May 2003:
Over 1,000 people are killed and nearly
7,000 hurt in a quake in Algeria,
which measured 6.7 on the Richter scale.
 

March 2002:
Thousands die in a remote area of Afghanistan
after an earthquake measuring 6.0 on the Richter scale.
 

January 2001:
30,000 people die and more than 50,000 are injured
by an earthquake measuring 7.9
on the Richter scale in Gujarat, India.

January 2001:
1,000 people die in a 7.2 earthquake in El Salvador.
 

Why is it dangerous after a quake?

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.

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