An earthquake is caused by a sudden slip on a fault. Faults are thin zones of crushed rocks, which separate blocks on the earths crust. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.
These few seconds of shaking can lead to a whole lot of damage.
These few seconds of shaking can lead to a whole lot of damage.