Scientists recreate quakes in lab

In nature, they occur hundreds of kilometres below the surface and scientists say that they should not actually happen.

Understanding deep faulting will significantly improve our knowledge of Earth science.

The results have also helped explain the origin of some of the largest and most violent earthquakes to occur on Earth.

Most earthquakes occur in the top 30-100 kilometres of the Earth's crust.

The crust is cold, at low pressure, and therefore brittle, so when rocks suddenly fall an earthquake occurs.

Deep earthquakes occur below subduction zones 100-650 km beneath the Earth's surface.

Here the Earth is so hot that rocks should simply flow past each other instead of producing the jolts that cause earthquakes.

But these flowing rocks come under very high pressures and when these deep earthquakes occur, the energy released can be very large.

Chemical reactions

The largest deep earthquake ever registered was a magnitude 8.3 and occurred 600 km below Bolivia in 1994.

But scientists say that deep earthquakes should not happen as the rocks flow over each other.

They are thought to be triggered by various chemical reactions which happen in subduction zones.

Subduction occurs when two tectonic plates move towards each other, with one block of rock being forced under the other.

This latest research was carried out at the Mineral Ice and Rock Physics Laboratory at University College, London, UK.

It is the first time scientists have been able to generate and observe deep earthquakes in the laboratory, recreating the exact pressure and temperature conditions of the deep Earth.

They have found that one theory, about dehydration inducing deep seismic activity, works in principle.

Dr David Dobson from University College, London who led the research told BBC News Online that understanding deep faulting would significantly improve our understanding of how the Earth works.

He said: "Deep and intermediate focus earthquakes are an important and mysterious class of earthquakes. Understanding these deep earthquakes could be the key to unlocking the remaining secrets of plate tectonics.

"Although plate tectonics is a remarkably powerful theory, we still after 40 years don't understand the driving forces behind plate motions."