A massive earthquake struck in the Sichuan province in China on May 12th. It had a magnitude of 7.9 on the Richter scale, and was large enough to be felt in Bangkok, Thailand, which is more than 1,800 kilometers (1100 miles) away. More than 50,000 people have died.
What causes earthquakes? Scientists believe that the Earth’s surface consists of a hard shell called the crust, which is broken into large pieces called plates. Continents and oceans lie on top of these plates, as shown in the image. Below these plates is very hot liquid rock called magma. The plates are floating on top of this magma and are constantly moving at very slow speeds (around 5 to 10cm a year). Some plates are moving away from each other causing magma to bubble up and create new land or sea bed. Some plates are moving towards each other and pushing each other. This can create mountains and cause existing mountains (including Mount Everest) to keep getting taller. Some plates are sliding next to each other and this friction causes earthquakes. The magnitude of an earthquake is measured on the Richter scale, and is determined by how much the earth shakes. Usually, a magnitude of 6 and above is considered to be a strong earthquake. Also, each one-point increase on the scale indicates ten times the amount of shaking! The largest recorded earthquake in the world was a magnitude 9.5 in Chile in 1960.