If I am correct (it has been a while since I've learned about this) an earthquake is caused by two tectonic plates rubbing against each other which causes the land to shake violently until they stop moving. The pressure of magma under the plates causes them to shift and collide. The evidence it provides is magma from mantle builds pressure causing the tectonic plates that are part of the crust (the part we live on) to shift.
I hope I explained this well. I'm sorry if it's wrong, it's been about 4 years since I learned about this. However I'm sure this is correct.