There are different ways of measuring an earthquake. It is intensity and magnitude what usually measured. Intensity is the degree of destruction caused by the earthquake on the surface. Magnitude is the degree of intensity, the dimension proportionate to the seismic waves energy thrown out during the earthquake.
For measuring the magnitude, Richter scale is used. It is called after an American seismologist Charles F. Richter (1900–1985). Richter scale , measure of the magnitude of seismic waves from an earthquake, devised in 1935 by the American seismologist Charles F. Richter (1900–1985). Magnitude is measured in 9 grade scale. Mercalli scale is used to measure the consequencies of an earthquake connected with human victims and building destruction. This scale was invented by an Italian seismologist Joseph Mercalli. In many countries an international scale MSK-64, which measure all earthquakes in 12 grades, is used.
The earthquake intesity is measured with an instrument called seismograph. It is a set of devices that register the tremor of ground during an earthquake. These tremors are trasformed in an electronic signal, recorded on the seismograms, the graphic record, in analogic or digital format. A most sensitive seismograph has a pendulum or a magnet with a heavy mass. On the earth's surface and under sea, over 2 thousand seismograph are set. Please, click this image to see how a seismograph works.