Earthquakes are a fascinating phenomenon—unless you happen to be standing at the epicentre of one. Some tremors are so minor they barely register on the Richter scale, whereas others cause widespread devastation and loss of life. So how are earthquakes formed?
Earthquakes are caused by a movement in the earth’s crust that is followed by a release in energy.
How are earthquakes formed by plate tectonics?
The theory underpinning the science of earthquakes is known as Plate Tectonics. Scientists now know the earth’s crust is made up of a series of plates that are continuously moving on a layer of soft rock known as mantle. Every once in a while, the edges of plates rub against each other and pressure builds up. Once the build up of stress is enough to cause the crust to break or move, the pressure is released in a series of seismic waves. The waves shake the earth and we experience what is known as an earthquake.
Whilst our ancestors probably thought the shaking and trembling of the ground was the act of a vengeful god, earthquakes are definitely no random event. By 1962, scientists had come to the conclusion that earthquakes could be linked to the way pieces of the earth’s crust moved around and a map was drawn up to illustrate where the boundaries of the plates occurred. Although earthquakes can occur anywhere, they generally happen more frequently along the edges of plates and there are some parts of the world renowned for having a major fault line in the earth’s crust—for example, the San Andreas Fault in California.
How are earthquakes formed at transform plate boundaries?
Plate boundaries are the location for a great deal of activity, and not just earthquakes. Plates move together in different ways: they can slide by, move away, or move towards each other. Transform plate boundaries are where two plates slide alongside each other and are fairly rare on continental land masses; the San Andreas Fault is an example of a transform plate boundary. Earthquakes along a transform plate boundary are usually shallow and frequent.
How are earthquakes formed under the sea?
Earthquakes are very common beneath the sea. Quite often, the only outward sign of an earthquake occurring on the seabed is a tsunami (giant wave). But while seabed earthquakes might seem less damaging than those that affect urban areas, tsunamis can be just as devastating, as was seen in the 2004 Indian Ocean Boxing Day Tsunami when more than 300,000 people lost their lives.
The center of an earthquake is known as the epicenter and the depth of the epicenter makes a difference to the amount of damage caused as the shallower the earthquake, the more damage there is likely to be to buildings.
How are earthquakes measured?
A device known as a seismometer measures the magnitude of an earthquake. You would probably not even feel an earthquake with a magnitude of 3 or less, but an earthquake of 7 or greater is likely to cause considerable damage to structures in the area.