Education: earthquakes
Learn about earthquakes and tsunamis – and how these two natural disasters are linked
SOME earthquakes cause great destruction: buildings collapse and many people are hurt or even killed. Other quakes are so slight you can hardly feel them. But what causes the earth to shake? Let’s find out.
WHAT CAUSES AN EARTHQUAKE?
Earth consists of various layers. At the centre of the planet is the inner core and around it is the outer core. Around the outer core is the mantle and around that is Earth’s crust.
Earthquakes occur in the crust – the planet’s thinnest layer. The crust, which is about 40 km deep, includes the ground we live on and the seabed.
Earth’s crust and the upper part of the mantle are divided into various parts known as tectonic plates, which fit together like jigsaw-puzzle pieces. These plates are about 125 km thick and are moving all
the time but so slowly that we can’t feel it. The places where the plates meet one another are called faults. Sometimes the edges of plates get stuck against each other while the rest of the plates continue to move.
When enough pressure has built up, the plates suddenly slide faster. Sometimes one plate moves over another or one breaks, causing an earthquake. This can cause much damage such as making buildings collapse.
The place under Earth’s surface where the earthquake originates is called the hypocentre. The place on Earth’s surface directly above the hypocentre is known as the epicentre. This is where the earthquake is most severe.
Smaller earthquakes can usually be felt before and after severe quakes. These are called foreshocks and aftershocks. They can take place a few hours or even a few months before or after a severe earthquake.
WHERE DO EARTHQUAKES OCCUR?
Earthquakes occur where tectonic plates meet (as mentioned earlier) or at weak points in the tectonic plates. Most earthquakes (about 90 percent) take place within a region on Earth known as the Ring Of Fire. This region extends almost like a belt around the Pacific Ocean and includes countries such as New Zealand, Indonesia and Japan, and the west coasts of North and South America.
In countries where earthquakes are common, such as Japan and Turkey, buildings are designed to better withstand them. An example of such buildings is the Sabiha Gökçen International Airport in Istanbul, Turkey. Istanbul is located where three large tectonic plates meet so chances are an earthquake will occur there. The airport is designed to withstand a quake measuring eight on the Richter scale.
The Utah State Capitol building in the USA is also earthquake-resistant – it has rubber isolators in its foundations. The idea is that during an earthquake these isolators will allow the building to rock gently to and fro, so the foundation moves but not the structure on top of it.
WHICH WAS THE BIGGEST EARTHQUAKE IN HISTORY?
An earthquake in Chile on 22 May 1960 measured 9,5 on the Richter scale. There were foreshocks measuring more than seven. The quake caused a tsunami that travelled across the sea at more than 300 km/h.
It’s impossible to obtain detailed information on earthquakes that occurred before 1900 because until then scientists didn’t have the instruments needed to make accurate measurements.