# Richter magnitude scale

Richter scalemagnitudeRichter magnitudeM L Richterlocal magnitudescalemajor earthquakeLocal magnitude scaleRichter magnitudes
The so-called Richter scale – also Richter magnitude or Richter magnitude scale, more accurately but informally Richter's magnitude scale – for measuring the strength ("size") of earthquakes refers to the original "magnitude scale" developed by Charles F. Richter and presented in his landmark 1935 paper.wikipedia
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### Charles Francis Richter

Charles RichterCharles F. RichterRichter, Charles Francis
The so-called Richter scale – also Richter magnitude or Richter magnitude scale, more accurately but informally Richter's magnitude scale – for measuring the strength ("size") of earthquakes refers to the original "magnitude scale" developed by Charles F. Richter and presented in his landmark 1935 paper.
Richter is most famous as the creator of the Richter magnitude scale, which, until the development of the moment magnitude scale in 1979, quantified the size of earthquakes.

### Moment magnitude scale

moment magnitudeM w magnitude
Because of various shortcomings of the ML scale most seismological authorities now use other scales, such as the moment magnitude scale, to report earthquake magnitudes, but much of the news media still refers to these as "Richter" magnitudes.
The moment magnitude scale (MMS; denoted explicitly with M or Mw, and generally implied with use of a single M for magnitude ) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment (a measure of the "work" done by the earthquake ), expressed in terms of the familiar magnitudes of the original "Richter" magnitude scale.

### Logarithm

logarithmsloglogarithmic function
All magnitude scales retain the logarithmic character of the original and are scaled to have roughly comparable numeric values. First, to span the wide range of possible values, Richter adopted Gutenberg's suggestion of a logarithmic scale, where each step represents a tenfold increase of magnitude, similar to the magnitude scale used by astronomers for star brightness.
This is used in the moment magnitude scale or the Richter magnitude scale.

### Beno Gutenberg

Gutenberg, BenoB. GutenbergGutenberg
Richter resolved some difficulties with this method and then, using data collected by his colleague Beno Gutenberg, he produced similar curves, confirming that they could be used to compare the relative magnitudes of different earthquakes.
He was a colleague and mentor of Charles Francis Richter at the California Institute of Technology and Richter's collaborator in developing the Richter magnitude scale for measuring an earthquake's magnitude.

### California Institute of Technology

CaltechCalifornia Institute of Technology (Caltech)Cal Tech
Wood then built, under the auspices of the California Institute of Technology and the Carnegie Institute, a network of seismographs stretching across Southern California.
Seismologist Charles Richter, also an alumnus, developed the magnitude scale that bears his name, the Richter magnitude scale for measuring the power of earthquakes.

### Rossi–Forel scale

Rossi-Forel scaleRossi–Forel intensity
Prior to the development of the magnitude scale, the only measure of an earthquake's strength or "size" was a subjective assessment of the intensity of shaking observed near the epicenter of the earthquake, categorized by various seismic intensity scales such as the Rossi-Forel scale.

### Surface wave magnitude

M s magnitudesurface wave
In 1956, Gutenberg and Richter, while still referring to "magnitude scale", labelled it "local magnitude", with the symbol, to distinguish it from two other scales they had developed, the surface wave magnitude (M S ) and body wave magnitude (M B ) scales.
Surface wave magnitude was initially developed in the 1950s by the same researchers who developed the local magnitude scale M L in order to improve resolution on larger earthquakes:

In 1931 Kiyoo Wadati showed how he had measured, for several strong earthquakes in Japan, the amplitude of the shaking observed at various distances from the epicenter.
It was Wadati's 1928 paper on shallow and deep earthquakes, comparing maximum below surface displacement against distance from the epicentre, which led Charles Richter to develop his earthquake magnitude scale in 1935.

### Modified Mercalli intensity scale

Mercalli intensityMercalli intensity scaleMMI
The Richter and MMS scales measure the energy released by an earthquake; another scale, the Mercalli intensity scale, classifies earthquakes by their effects, from detectable by instruments but not noticeable, to catastrophic.
Not wanting to have this intensity scale confused with the magnitude scale he had developed, he proposed calling it the "Modified Mercalli scale of 1956" (MM56).

### 1935 in science

1935
* Charles Richter and Beno Gutenberg develop the Richter magnitude scale for quantifying earthquakes.

### Microearthquake

Micromicro earthquakesMicroearthquakes
A microearthquake (or microquake) is a very low intensity earthquake which is 2.0 or less in magnitude.

### Seismic moment

moment
The seismic moment, M_o, is proportional to the area of the rupture times the average slip that took place in the earthquake, thus it measures the physical size of the event.

### Seismometer

seismographseismographsseismometers
In the 1920s Harry O. Wood and John A. Anderson developed the Wood–Anderson Seismograph, one of the first practical instruments for recording seismic waves.

### Seismic intensity scales

seismic intensity scale
Prior to the development of the magnitude scale, the only measure of an earthquake's strength or "size" was a subjective assessment of the intensity of shaking observed near the epicenter of the earthquake, categorized by various seismic intensity scales such as the Rossi-Forel scale.

### John Milne

Milne, JohnJ. MilneMilne
In 1883 John Milne surmised that the shaking of large earthquakes might generate waves detectable around the globe, and in 1899 E. Von Rehbur Paschvitz observed in Germany seismic waves attributable to an earthquake in Tokyo.

### Harry O. Wood

Harry Wood
In the 1920s Harry O. Wood and John A. Anderson developed the Wood–Anderson Seismograph, one of the first practical instruments for recording seismic waves.

### John August Anderson

John A. AndersonDr. J.A. AndersonJ.A. Anderson
In the 1920s Harry O. Wood and John A. Anderson developed the Wood–Anderson Seismograph, one of the first practical instruments for recording seismic waves.

### Carnegie Institution for Science

Carnegie Institution of WashingtonCarnegie InstitutionCarnegie Institute
Wood then built, under the auspices of the California Institute of Technology and the Carnegie Institute, a network of seismographs stretching across Southern California.

### Southern California

southernSoCalCalifornia
Wood then built, under the auspices of the California Institute of Technology and the Carnegie Institute, a network of seismographs stretching across Southern California.

### Apparent magnitude

apparent visual magnitudemagnitudevisual magnitude
First, to span the wide range of possible values, Richter adopted Gutenberg's suggestion of a logarithmic scale, where each step represents a tenfold increase of magnitude, similar to the magnitude scale used by astronomers for star brightness.

### Micrometre

μmµmmicrometers
Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in microns", measured at a distance of 100 km.

### Attenuation

attenuateattenuatedattenuating
The Richter scale was defined in 1935 for particular circumstances and instruments; the particular circumstances refer to it being defined for Southern California and "implicitly incorporates the attenuative properties of Southern California crust and mantle."

### Hypocenter

hypocentrefocusfocal depth
The reason for so many different ways to measure the same thing is that at different distances, for different hypocentral depths, and for different earthquake sizes, the amplitudes of different types of elastic waves must be measured.