An earthquake sends shock waves rippling through the ground. Scientists study these waves to see how big earthquake is. They measure earthquakes on a scale of 1 to 10. Each quake on the scale is 30 times worse than the one before

Tectonic plates What makes an earthquake happen? Planet Earth is covered with a thick crust. The crust is cracked into more than twenty sections – a bit like the shell of a boiled egg when you tap it with a spoon.

Tectonic plates Earthquakes happen all the time in all parts of the world but we don’t notice them because they are small. These cracked sections are called tectonic plates and they are always on the move. They move very slowly, but with incredible power. When the plates rub against each other or collide with each other, an earthquake happens.

NO PROTECTION Nowadays, new buildings in earthquake-prone towns and cities are built to withstand the shock of an earthquake. Even so, during seismic activity, gas pipes and electricity cables are ripped apart and cause fires and explosions, so even if buildings don’t fall down, there can still be a lot of destruction.

NO PROTECTION San Francisco sits on one of the greatest earthquake zones in the world. Children have earthquake drills at school, but, unsurprisingly, people hope that it will never happen and are still building new houses, shops and office blocks.

TSUNAMI A tsunami is a chain of huge waves, again caused by an earthquake, but this time under the seabed. Tsunami waves can be very long (as much as 100km) and there may be an hour between them.

TSUNAMI They can move very fast, too, sometimes at the speed of 800 kilometres an hour. When a tsunami reaches the coastline, it slows down but its height grows. There have been tsunami as high as 30 metres above the sea level!

TSUNAMI The Christmas weekend tsunami of 2004 is probably the most destructive one in the history. It was caused by an earthquake in the Indian ocean measuring 9.0 on the Richter scale. The huge waves crashed into several Asian countries and thousands of people lost their lives.

Sounding the Alarm These clever animals not only sensed the tsunami but saved many people. As they ran off the beach, they lifted tourists onto their backs with their trunks, taking them to a safe place. Before the huge waves of the recent tsunami crashed into the coastline areas, wild and domestic animals showed very unusual behaviour.They seemed to know what was going to happen. Do animals have a sixth sense? Can they predict disasters? And why don’t people learn to use these animal instincts?

Sounding the Alarm According to eyewitness stories, the following events happened: Elephants screamed and ran for higher ground. Dogs refused to go outdoors. Zoo animals rushed into their shelters and nothing could make them come out.

Sounding the Alarm  Such stories aren’t new. In 373 BC, historians wrote that animals, including rats and snakes, deserted the Greek city of Helice just days before a quake destroyed the place.  During the more recent earthquake in Turkey in 1999, dogs howled like wolves for two days before earthquake struck. No one took any notice and many buildings fell down like stacks of cards, killing over 17,000 people