SCDO - Earthquakes Earthquakes Earthquakes are a shaking or trembling of the Earth's crust caused by the release of huge stresses due to underground volcanic forces, the breaking of rock between the surface, or by a sudden movement along an existing fault line.
Earthquakes are unpredictable and strike without warning.
They range in strength from slight tremors to great shocks lasting from a few seconds to a few minutes. There is no upper limit to this scale as there is no upper limit to the amount of energy an earthquake might release. The most severe earthquakes recorded so far have not exceeded 9.5 on the Richter Scale. In the last 80 years there have been 17 earthquakes in Australia registering 6 or more on the Richter Scale. Australia's rate of earthquakes is about 1 every 5 five years, compared to a world average of about 140 per year.