The Richter Scale

The Richter scale is logarithmic, that is an increase of 1 magnitude unit represents a factor of ten times in amplitude. The seismic waves of a magnitude 6 earthquake are 10 times greater in amplitude than those of a magnitude 5 earthquake. However, in terms of energy release, a magnitude 6 earthquake is about 31 times greater than a magnitude 5.

The magnitude of an earthquake is a measure of the amount of energy released. Each earthquake has a unique magnitude assigned to it. This is based on the amplitude of seismic waves measured at a number of seismograph sites, after being corrected for distance from the earthquake. Magnitude estimates often change by up to 0.2 units, as additional data are included in the estimate.

The intensity of an earthquake varies greatly according to distance from the earthquake, ground conditions, and other factors. The Modified Mercalli Intensity Scale is used to describe earthquake effects.
(Note: Though, the above link fails to even mention the words Tsunami or Tidal waves!)