Follow the links below to read more about Earthquakes on Epic!:
PDF LINK: Earthquake – Recovering Together After a Natural Disaster by the Queensland Government
Earthquakes
VIDEO: Earthquake 101 - National Geographic
VIDEO: Behind the News - 2015 Nepal Earthquake
WHAT IS AN EARTHQUAKE?
Earthquakes are the shaking, rolling or sudden shock of the earth’s surface. They are the Earth's natural means of releasing stress. More than a million earthquakes rattle the world each year. Earthquakes can be felt over large areas although they usually last less than one minute.
So, the ground beneath us is constantly moving. Sometimes the movement is sudden and very powerful. When this occurs it is called an earthquake.
Earthquakes can be very destructive and often result in damage to buildings and loss of life. Fortunately, earthquakes of this magnitude are quite rare in Australia. Other countries are not so lucky.
Map of the world, showing the tectonic plate boundaries and the names of the plates
Map of the World, showing the shape of the continents
PLATE TECTONICS
The theory of plate tectonics explains why seismic activity (the movement of the ground) is both more frequent and more severe in particular regions of the world. The plate tectonic theory explains why some regions are prone to earthquakes. This theory describes how the Earth's crust is made up of a number of large plates which are slowly but continually moving.
New Zealand, for example, sits above the point where two of these plates meet. Australia, on the other hand, sits right in the middle of a plate. Therefore New Zealand has more frequent and severe Earthquakes than Australia.
Tectonic plates drift on the liquid rock, slowly changing shape and position over time. At the plate boundaries the earth's crust is constantly being created and destroyed.
Look at the world map to the left. If we could slide South America towards Africa, do you think the two landmasses would fit together like a jigsaw puzzle?
CONTINENTAL DRIFT
-
In 1910, a German scientist called Alfred Wegener, was the first to study the idea that the continents might have once been a single landmass. However, it wasn’t until 20 years after Wegener died, that geologists realised he was right.
-
The continents and ocean floors really do “float” on moving rock plates, and have been drifting for millions of years.
-
Wegener looked at where different fossils were found and was able to piece the continents back together into one landmass.
-
250 million years ago, all the land on Earth was one large landmass. Wegener named this landmass Pangaea.
-
The moving tectonic plates started to split Pangaea apart. The plates move about 1 to 10 cm every year. They can move towards each other, away from each other or rub alongside each other.
Alfred Wegener
What scientists believe Pangaea may have looked like
WHAT CAUSES AN EARTHQUAKE?
There are about 20 plates along the surface of the earth that move continuously and slowly past each other. When the plates squeeze or stretch, huge rocks form at their edges and the rocks shift with great force, causing an earthquake.
Think of it this way: Imagine holding a pencil horizontally. If you were to apply a force to both ends of the pencil by pushing down on them, you would see the pencil bend. After enough force was applied, the pencil would break in the middle, releasing the stress you have put on it. The Earth's crust acts in the same way.
As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy which moves through the Earth in the form of waves, which we feel and call an earthquake.
