Richter magnitude scale

The Richter scale assigns a single number to quantify the amount of seismic energy released by an earthquake. The scale uses a base-10 logarithm by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a particular type of seismometer. A earthquake measuring 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0.
The moment magnitude, calibrated to give generally similar value for medium-sized earthquakes, scale has replaced the Richter scale. The moment magnitude scale reports a fundamental property of the earthquake derived from instrument data and also does not saturate in the high-magnitude range.

Charles Richter and Beno Gutenberg developed the scale first to be used only in one particular study. He was trying to create a machine that could separate the vastly larger number of smaller earthquakes from the few larger earthquakes observed in California at the time.
He was inspired by the apparent magnitude scale used in astronomy and arbitrarily chose a magnitude of 0 to be an earthquake that would show a maximum combined horizontal displacement of 1 µm. He did this in order to prevent negative magnitudes from being assigned; however, the Richter scale has no actual lower limit.

When a earthquake is larger than 6.8 on a single seismograph the values saturate and cannot increase for more powerful earthquakes. Gutenberg and Ricther developed a magnitude scales based on surface waves, surface wave magnitude MS, and another based on body waves, body wave magnitude mb.

Older magnitude scales have been replaced by the implementation of methods for estimating the seismic moment. A logarithm of the amplitude of waves recorded by seismographs is used to determine the Richter magnitude of an earthquake.

Each increase in magnitude equates to an amplitude of about 31.6 time the amount of energy released, while an increase of 0.2 corresponds to a doubling of the energy released. Seismographs all over the world can detect a earthquake with a magnitude of 4.6 or greater as long as the seismograph is not within the earthquake’s shadow.

Large earthquakes occur once a year, on average, while the largest recorded was the Great Chilean Earthquake of May 22, 1960 which had a magnitude of 9.5.