What is a Richter magnitude scale?

The Richter magnitude scale, also known as the local magnitude (M_L) scale, assigns a single number to quantify the amount of seismic energy released by an earthquake. It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitudeof the largest displacement from zero on a Wood–Anderson torsion seismometer output. So, for example, an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0. The effective limit of measurement for local magnitudeM_L is about 6.8.

Though still widely used, the Richter scale has been superseded by the moment magnitude scale, which gives generally similar values.

The energy release of an earthquake, which closely correlates to its destructive power, scales with the ³⁄₂ power of the shaking amplitude. Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 ( = (10^1.0)^{(3 / 2)}) in the energy released; a difference in magnitude of 2.0 is equivalent to a factor of 1000 ( = (10^2.0)^{(3 / 2)} ) in the energy released.^[1]