Living With Earthquakes
Where Earthquakes Occur & Why
Earthquakes happen along and near the boundaries of the tectonic plates. These plates are large sections of the Earth's crust that move at different speeds and in different directions, sometimes colliding, passing under one another and crushing or sliding past each other.
Tension builds up between plates when they become jammed or grate together, and this tension is released as a burst of shaking energy - an earthquake. There are a number of types of boundaries, and earthquakes take place along them for different reasons. The First type is a collision zone, where two tectonic plates, made of continental crust collide, and because they are of the same density, they create, either a deep trench, or a high mountain range. An example of such a boundary would be the collision zone between the Indo-Australian Plate and the Eurasian plate, at the Himalayas.
Earthquakes happen here because the crust has crumpled and there is a great amount of tension.
Another type is a constructive margin. Here, when two Oceanic Plates move away from one another, magma rises to the surface, creating new crust. A good example of this type is the Mid-Atlantic Rift. Earthquakes occur here because there is friction between plates.
Another variety is a Destructive margin, such as the one between the South American Plate and the Nazca Plate. This is when dense Oceanic Crust sinks down beneath less dense Continental Crust, and re-melts to become part of the mantle. Earthquakes happen here because of friction between the plates as one moves under the other. These earthquakes can happen hundreds of miles away from the plate boundary, as the oceanic crust grates along underneath.
The final type is a Conservative Margin. This is when two plates move past each...