Earthquakes are measured with a device called a seismograph. The Richter scale measures the magnitude (size) of an earthquake on a scale of 1 to 10 using a seismograph. Each step in the scale indicates a tenfold increase in the energy of the earthquake.
The Richter scale was devised in the 1930s by an American geophysicist called Charles Richter (1900 - 1985). The most powerful earthquake ever recorded was in Chile in 1960, which regidtered 9.5 on Richter scale.
Between 10 and 20 earthquakes each year reach 7 on the Richter scale.
The Modified Mercalli scale assesses an earthquake's severity according to its effects on a scale of 1 to 12 in Roman numerals (I - XII). A Mercalli scale I earthquake is one that is only detectable with special instruments. A Mercalli scale XII earthquake causes almost total destruction of cities and reshapes the landscape.