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Earthquakes - Get the facts
Earthquakes are unpredictable and can occur at any time.
There is at least one earthquake that occurs somewhere in the world each day. Some can be slight tremors that can hardly be felt, while others can be much stronger.
Earthquakes happen because the Earth’s tectonic plates are always moving and floating on molten rock. An earthquakes can last from a few seconds to a few minutes, which can be followed by after-shocks.
Measuring Earthquakes
The magnitude of an earthquake is measured and recorded by a device called a seismograph, which uses the Richter Scale.
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A seismograph
The Richter Scale has no upper limit to being able to record the magnitude of an earthquake. The most severe earthquakes so far, have not exceeded 9.5 on the Richter Scale.
The Richter Scale uses complex mathematics to calculate the magnitude of an earthquake. For instance, a magnitude 7.0 creates 10 times the ground motion of a magnitude 6.0 earthquake and the total energy release is about 30 times greater. This in turn is 30 times greater than a 5.0 and so on.
Another scale used to describe earthquakes is the Modified Mercalli (MM). It rates the amount of intensity, shaking felt and damage caused, and uses Roman numerals. On this Scale, I = a barely detectable tremor, and XII = total damage.
Did you know?
- In Australia, an earthquake of Richter magnitude 5.5 (ie: almost that of the Newcastle event in 1989) occurs every 15 months on average.
- 90% of all earthquakes in the World take place at plate boundaries and are the result of the constant movement of the plates against each other.
- The geographically-oldest western and central parts of Australia, are most seismically active.
- The 1989 Newcastle Earthquake has been Australia's most damaging earthquake with 13 fatalities and insured damage of $1,124 million.
- The most deadly earthquake was recorded in China in 1557. During this time many people lived in the mountains in artificial caves and the quake resulted in over 800,000 deaths.