anyone who has been in earthquake has felt that it was one of the scariest and most disturbing experience of their life.Have you ever been in an earthquake? After anearthquake in Adana in June 1998 , A group of students from Ataturk Lisesi went to find out . Julie Trebble a seismologist working in Turkey,anwered their questions.
What exactly is an earthquake?
Let me try to explain.Hold this stick Now,bend in gently .when you release the pressure the stick returns to its original shape. Now do the same but with a lot of perssure. Crack! the stickehas broken.Excuse me,but what's that got to do with an earthquake?
I'm coming to that. About 15 kilometres underground there are lot of rocks. Pressure makes the rock move all the time.when there is little pressure,they go back to their place ,like the stick but when the pressure is too strong ,the rocks break.like the stick,they make a noise-crake ! That's the earthquake itself.What makes the ground move?
The friction of the rocks against each other produces vibrations.these are called seismic waves . The waves come to the surface. This is what makes the ground shake.The strongest waves can destroy buildings. The weakest make the ground shake only a little and often we can't even feel it. But we use a special instrument which registers even the tiniest seismic waves.This is called a seismograph. That's how we khow there are thousands of earthquake ever month. Maybe there has just been one and we haven't felt it.
There is something I haven't understood very well. Where does the pressure on the rocks come from?
Well , under the crust of the Earth, there are thousands of kilometres of molten rock and metal.They are very hot and under very high pressure.Think of a saucepan with water.You heat it and ,when it boils ,the lid shakes because of the intense heat coming up.Well , it's someting like that.The heat rises from the centre of earth so the surface rattles,like the lid of the saucepan.
Why are earthquakes stronger in some places than others?
The crust of the Earth is divided into enormous plates.They look like the pieces of a jigsaw. When the pressure from centre gets very strong.the plates bang against each other.The places nearest the violent earthquakes. They are the most fragile place on Earth.
How long does an earthquake last?
The breaking of the rocks,the earthquake itself ,only lasts a fraction of a second . An earthquake may last about 15 seconds and up to one minute when it is very strong or when you are near the place where the seismic waves reach the surface.That place is called the epicentre of the earthquake.
What is the Ricther scale?
Charles Ricther was an American seismologist who studied earthquakes in California. In 1935 ,he invented a method to measure the amount of energy produces by and earthquake. This is called its magnitude. Richter used a scale from 1 (the lightest) to 10 (the strongest). One of is worst earthquakes in history happened in Chile in 1960 . It measures 9 on the Ricther scale. Another one , in Mexico City in 1985, killed thousand of people . It measured 8.5 and lasted for nearly a minute.