To help resolve the question betweenthese two possibilities, Heaton turned to other subduction zones--such as those in southern Chile, southwestern Japan and Colombia--that also have young, relatively slow oceanic plates diving under a continental plate
. "By comparing this zone with other areas around the world,' says Heaton, "we've come to the conclusion that the places that look most similar to this zone have, in fact, had large earthquakes.'
"The earth is divided into continental plates
and these plates move.
About half of the world's subduction zones, which typically lie in deep water far offshore, are considered erosive margins, where the ocean-crust plate is scouring the front edge of the overriding continental plate
, says Francesca Remitti, a geologist at the University of Modena and Reggio Emilia in Italy.
In the fourth type, called collision, two continental plates
crash into each other, forming high mountains.
These volcanoes are often fed with magma that mixes with continental plate
material, which holds loads of silica.
Pakistan and the region, along an active continental plate
boundary, is often hit by earthquakes.
Cawood suggested that this stability may have been due to the gradual cooling of the earth's crust over time and he said that before 1.7 billion years ago, the Earth's crust would have been substantially hotter, meaning that continental plate
movement may have been governed by different rules to those that operate today.
The ex-politician began exploring the Finnish side of what is known as a craton - a large section of continental plate
- after Russians discovered one of the world's biggest diamond mines on their side of the same rock formation.
A continental plate
boundary; tectonics at South Island, New Zealand.
The zone is a fault line where two giant tectonic plates - the Juan de Fuca and North American, or continental plate
- are locked tightly against each other.
It may look all right with the small features of a continental plate
but with Britain's bold registration characters, it sticks out like a sore thumb on the nearside valance.