Understanding the Vanuatu M 7.3 earthquake

Which are Nature's triggers for the massive Vanuatu earthquake from August 10,2010 ?

Courtesy : Wikipedia and USGS

Courtesy : Wikipedia and USGS

In plate tectonics, a convergent boundary also known as a destructive plate boundary (because of subduction), is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another and collide.
s a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries.
When two plates move towards one another, they form either a subduction zone.
This depends on the nature of the plates involved. In a subduction zone, the subducting plate, which is normally a plate with oceanic crust, moves beneath the other plate, which can be made of either oceanic or continental crust.

When two plates with oceanic crust converge they typically create an island arc as one plate is subducted below the other. The arc is formed from volcanoes which erupt through the overriding plate as the descending plate melts below it.
The arc shape occurs because of the spherical surface of the earth (nick the peel of an orange with a knife and note the arc formed by the straight-edge of the knife).

A deep undersea trench is located in front of such arcs where the descending slab dips downward, such as the Mariana trench near the Mariana Islands. Other good examples of this type of plate convergence would be Japan and the Aleutian Islands in Alaska.
The Vanuatu trench near the island of Efate can be seen very clearly on the satellite maps below.
When both of the plates are made of oceanic crust, convergence is associated with island arcs such as the Solomon Islands.

Main source text and graphics :  Wikipedia