What causes an earthquake?
We feel an earthquake when seismic waves travel through the ground beneath our feet. Seismic waves travel through rocks in the earth’s crust much like ripples spread across the surface of a still pond after dropping in a rock. A cork floating on the pond will bob up and down when the spreading ripples pass beneath it. Although seismic waves in the earth travel much faster than ripples on a pond (and have some other fundamental differences also), it is the passage of seismic waves that causes the shaking motion we feel as an earthquake. Sudden slippage along fractures in the earth’s crust (faults) causes seismic waves to form, which then radiate away in all directions. The greater the amount of slippage along a fault, the stronger the seismic waves. Like other forms of energy that travel as waves (sound and light for example), seismic waves lose energy as they spread out through the earth away from their source. This explains why damage caused by a large earthquake is generally greatest
