The surface of the earth is divided into seven major and eight minor plates. Major and minor tectonic plates Each plate is in motion relative to its neighbours, resulting in geological activity at the plate boundaries.

Convergent margins behave differently depending on whether the lithospheric plates involved are oceanic, continental or one of each. As oceanic lithosphere cools, it becomes denser, and the further away from the plate boundary it moves, the thicker it becomes.

An online resource from the Geological Society, outlining the three types of plate boundary and the activity that characterises them.

An online resource from the Geological Society, aimed at students aged 14 - 16. Learn how the theory of plate tectonics has developed, what happens at different plate margins, and the tectonic history of the UK.

At this time Tethys Ocean floor would have been subducting northwards beneath Asia and the plate margin would have been a Convergent oceanic-continental one just like the Andes today.

As the plate heats up the water is liberated, lowering the melting point of the mantle and causing partial melting. This produces magma, which rises and may be erupted explosively as andesite at the surface.

Whilst most tectonic activity is focused on plate margins, it is possible for earthquakes and volcanoes to occur far from the edges of tectonic plates. The causes of intraplate earthquakes are not fully understood.

At divergent plate margins, plates are moving apart and new lithosphere is being created. In the oceans, this has produced the mid ocean ridge system, which can also be described as a global range of underwater mountains.

The Pacific Plate is being moved north west due to sea floor spreading from the East Pacific Rise (divergent margin) in the Gulf of California. The North American Plate is being pushed west and north west due to sea floor spreading from the Mid Atlantic Ridge (divergent margin).

The Pacific plate moves towards the Okhotsk at around 8-9 cm/year which is pretty speedy for a tectonic plate and as the two moved past each other, the stresses in the crust built up until they were released in the earthquake.