Quake-slowing rocks found in Earth's crust

A team of scientists has discovered unusual rocks deep inside the Earth's crust that could slow down earthquakes.

Using computer models to create underground 3D images of the Chile earthquake (magnitude 8.8 on Richter scale) in 2010, researchers from the University of Liverpool found a mass of rocks, deep in the active fault line beneath Chile, that influenced the rupture size of the earthquake that struck the region.

The previously unknown structure is unusually dense and large for it to exist at that depth in the Earth's crust.

Further analysis revealed that it played a key role in the movement of the fault, causing the rupture to suddenly slow down.

"It was previously thought that dense geological bodies in an active fault zone may cause more movement of the fault during an earthquake," said Stephen Hicks, seismologist from the University of Liverpool in Britain.

"However, our research suggests these blocks of rock may, in fact, cause the earthquake rupture to suddenly slow down. But this slowing down can generate stronger shaking at the surface, which is more damaging to man-made structures," he concluded.

The research was published in the journal Earth and Planetary Science Letters.