... is not adequate for earthquake foci to be located and therefore it must change from a rock that can be easily fractured to a less easily fracturable rock. When an earthquake occurs, it produces waves that radiate out from the epicentre (The point on the surface directly above the focus). The body waves that are produced go into the earth. P-waves travel fastest with S-waves coming second, at half the speed. P and S-waves need dense, rigid rock to travel fastest in, as the rock gets less dense, the body waves slow down and when the rock turns to a liquid form, the S-waves cannot travel through and the P-waves are greatly decreased in velocity and refracted. As body waves travel into the earth, they enter the Moho, this area of crust is very dense and rigid and so both waves speed up rapidly. At approximately 50km, the waves suffer a ...

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