The first is the Crust or the Upper Mantle. This layer consists of the surfaces that we live on, the continents and land masses, to the basins of the oceans. It is up to 10 KM deep below the basins of the oceans and made up mostly of alumino-silicates.
Second is the Lower Mantle is 2900 KM thick and is where most of the earth's heat is stored, and much of the plate tectonic processes are driven. It is mostly made of ferro-magnesium silicates.
Next is the Outer Core is a liqiud layer 2300KM thick that is made of a nickel iron alloy. This layer is believed to control the earth's magnetic field.
And lastly the Inner Core a solid layer inside the outer core at 1200KM that is almost entirely iron.
All the layers are separated into two other "layers" call the lithosphere and the asthenosphere. The Lithosphere is made of the crust and the upper mantle. It had many that move in relation to each other due to tectonic forces. A tectonic force is the deformation of the earth's structures.
So what causes and Earthquake?
According to a UK Geology site, two forces can cause an earthquake:
one is volcanic activity
the second and most common is strong tectonic movement across faults and plate margins.
Next, what causes a volcano?
A volcano becomes active when two earth plates collide, one goes under the other and becomes very hot or molten and liquifies - magma. The magma needs oxygen from it's gas buildup so it finds a hole to the surface and erupts becoming lava. Lava can erupt up to 1600 degrees Farenheit, and when it cools, it turns into rock, which can expand land masses.
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