Seismologists use the Richter scale to express the energy released by an earthquake.
The earth movements during the earthquake are recorded on the seismograph as a diagram like the one below. The amplitude of the wave is used to calculate the magnitude.
The measuring scale is a logarithmical one, so a 5 degrees magnitude earthquake is 31 times stroger than a 4 degrees magnitude one.
The graph below shows how many times an earthquake of certain magnitude is more energetic than a 1 Richter degree earthquake.
The Mercalli Scale is used to measure the intensity of the earthquake. This intensity varies greatly according to distance from the earthquake, ground conditions, and other factors.