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Earthquake facts
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British Geological Survey
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Britannica earthquake information Your password is your Oxley student number
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Britannica tsunami information Your password is your Oxley student number
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What is an earthquake?
An earthquake is the sudden release of strain energy in the Earth’s crust, resulting in waves of shaking that radiate outwards from the earthquake source. When stresses in the crust exceed the strength of the rock, it breaks along lines of weakness, either a pre-existing or new fault plane. The point where an earthquake starts is termed the focus or hypocentre and may be many kilometres deep within the earth. The point at the surface directly above the focus is called the earthquake epicentre.
Vibrational energy is produced when rocks break; the energy spreads out in all directions like ripples on a pond. The shock waves radiate out from the point where the rocks first begin to break; this point is called the focus or hypocentre of the earthquake. The energy is dissipated as the shaking we call an earthquake.
Movements within the Earth’s crust cause stress to build up at points of weakness, and rocks to deform. When the stress finally exceeds the strength of the rock, the rock fractures along a fault, often at a zone of existing weakness within the rock.
Intense vibrations, or seismic waves, spread out from the initial point of rupture (the focus) like ripples on a pond. These waves are what makes the ground shake and can travel large distances in all directions. Near the focus, the waves can be very large, making them extremely destructive.
