Most large earthquakes on subduction zones occur because of

The sinking convection current of magma cause the oceanic plate and continential plate to collide,due to the fact that continential place is denser,it subducts under the less dense continential plate and lead to the formation of subduction zone

When the two plate collide, the pressure caused exceed the elastic strength of the rock, the rock then breaks and the ground vibrate,causing earthquake

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