How does the Richter scale measure earthquake size?

The Richter scale is a logarithmic measure of earthquake strength developed by Charles Richter and Beno Gutenberg in 1935. Although news media frequently use the term "Richter scale" for any earthquake measurement, seismological authorities now mostly use the moment magnitude scale because it avoids underestimating the energy of very large earthquakes. Magnitude scales measure inherent force using seismic waves, which differs from intensity scales that categorize local ground shaking effects.

What we know

• The original magnitude scale was presented by Charles Richter in collaboration with Beno Gutenberg in a landmark 1935 paper, later becoming known as the local magnitude scale. [2]
• The Richter scale uses common logarithms to make measurements manageable, where an increase from magnitude 3 to 5 corresponds to a hundredfold increase in seismic-wave amplitude. [2]
• Seismological authorities primarily use the moment magnitude scale for reporting large earthquakes because it relates more directly to energy and does not saturate or underestimate magnitudes. [4]
• Seismic magnitude scales differ from seismic intensity scales, which categorize the severity of ground shaking at a given location based on observed effects. [3, 5]

Where to go next

• whoWho were Charles Richter and Beno Gutenberg?
• compared withWhat is the moment magnitude scale?
• how it workedHow do seismographs record seismic waves?
• a case in pointHow does the Mercalli scale measure earthquake intensity?
• what caused itWhy do earthquakes happen?
• an unexpected connectionHow did a 1935 magnitude formula lead to modern media confusion?News outlets continue to broadcast measurements as Richter magnitudes long after scientific authorities transitioned to the moment magnitude scale.

Sources

• [1]Richter scale (Wikidata Q38768) · CC0 1.0
• [2]Richter scale · CC BY-SA 4.0
• [3]Seismic magnitude scales · CC BY-SA 4.0
• [4]Moment magnitude scale · CC BY-SA 4.0
• [5]Modified Mercalli intensity scale · CC BY-SA 4.0