Richter Scale | Universe Today

Written by Abby Cessna

Beichuan Region of China, before and after Earthquake. Image credit: Formosat 2

Richter magnitude scale is used to measure the size of earthquakes.  It is also known as the local magnitude scale and was created in 1935 by Charles Richter and Beno Gutenberg both from the California Institute of Technology. Originally, the scale was created in order to differentiate between the smaller and larger earthquakes observed in California.  At first, the scale only worked on one type of seismograph. That changed however, and now any calibrated seismograph can use the Richter scale. When Richter first designed the system, the size of the earthquakes was reported using quarter units. However, the system later changed to using decimals.

The Richter scale measures the amplitude of waves created by the earthquake then uses a logarithm to determine the numeric value of the earthquake. For every whole number increase in the scale, the amplitude of the quake is ten times greater. The Richter scale goes from zero with stronger earthquakes in higher numbers. The Richter scale does not have a higher limit. Generally, earthquakes below 2.0 on the Richter scale cannot even be felt; these are known as microearthquakes. Earthquakes between 2.0 and 3.9 almost never cause damage. Earthquakes between 4.0 and 5.9 can begin to cause damage while those 6.0 and above can start causing severe damage to the surroundings. An earthquake 10.0 or above on the Richter has never been recorded. The intensity of an earthquake and the damage it causes also depend on other factors, such as geological conditions and the distance to the origin of the earthquake.

As the quakes increase in magnitude on the Richter scale, they decrease in frequency. For example, around 8,000 microearthquakes are believed to occur each day. However, earthquakes that are between 8.0 and 8.9 on the Richter scale only happen about once a year. Some of these great earthquakes include the Sumatra earthquake in Indonesia in 2007, the 1960 Valvida earthquake in Chile, and the Mexico City earthquake in 1985.

A newer scale to measure earthquakes is the moment magnitude scale (MMS). This method, developed in the 1970’s, measures the earthquakes by how much energy they release. It uses the same values for the quakes that the Richter scale does; the new method is used by the United States Geological Survey to measure all new large earthquakes. For small earthquakes, however, the Richter scale is still generally used. Neither of these scales actually measure the intensity of the earthquake, meaning movement and damage caused by the earthquakes.

Universe Today has articles on the Torino scale and the biggest earthquake.

For more information, check out the Richter magnitude scale and the Richter scale.

Astronomy Cast has an episode on Earth.

Filed under: Astronomy