A scale that mathematically rates how much force an earthquake releases based on seismograph readings.

A scale that is used to compare the strength of earthquakes based upon the amount of energy released. The scale is logarithmic and an arbitrary earthquake was used as a starting point for creating the scale. As a result it is a continuous scale with no upper limit and negative numbers possible for very small earthquakes. An upper limit of approximately 9.0 is suspected as earth materials will most likely fail before storing enough energy for a larger magnitude earthquake.

A measure of an earthquake's size. It describes the total amount of energy released during an earthquake. In the 1930's, C.F. Richter devised a way measure the magnitude of an earthquake using an instrument called a seismograph to measure the speed of ground motion during an earthquake. Geologists discovered that the energy released in an earthquake goes up with magnitude faster than the ground speed by a factor of 32.

A scale that defines earthquakes on the basis of the amplitude of the largest ground motion recorded on a seismogram.

The Richter magnitude test scale (or more correctly local magnitude ML scale) assigns a single number to quantify the size of an earthquake. It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a seismometer output. Measurements have no limits and can be either positive or negative.